Add PosgreSQL dependencies to fix psycopg2 install error

[groovytron]

Error:

  - Installing psycopg2 (2.8.6)                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                               
[EnvCommandError]                                                                                                                                                                                                                                              
Command ['/var/www/app/.venv/bin/pip', 'install', '--no-deps', 'psycopg2==2.8.6'] errored with the following return code 1, and output:                                                                                                                        
Collecting psycopg2==2.8.6                                                                                                                                                                                                                                     
  Downloading https://files.pythonhosted.org/packages/fd/ae/98cb7a0cbb1d748ee547b058b14604bd0e9bf285a8e0cc5d148f8a8a952e/psycopg2-2.8.6.tar.gz (383kB)                                                                                                         
    Complete output from command python setup.py egg_info:                                                                                                                                                                                                     
    running egg_info                                                                                                                                                                                                                                           
    creating pip-egg-info/psycopg2.egg-info                                                                                                                                                                                                                    
    writing pip-egg-info/psycopg2.egg-info/PKG-INFO                                                                                                                                                                                                            
    writing dependency_links to pip-egg-info/psycopg2.egg-info/dependency_links.txt                                                                                                                                                                            
    writing top-level names to pip-egg-info/psycopg2.egg-info/top_level.txt                                                                                                                                                                                    
    writing manifest file 'pip-egg-info/psycopg2.egg-info/SOURCES.txt'                                                                                                                                                                                         
                                                                                                                                                                                                                                                               
    Error: pg_config executable not found.                                                                                                                                                                                                                     
                                                                                                                                                                                                                                                               
    pg_config is required to build psycopg2 from source.  Please add the directory                                                                                                                                                                             
    containing pg_config to the $PATH or specify the full executable path with the                                                                                                                                                                             
    option:                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                               
        python setup.py build_ext --pg-config /path/to/pg_config build ...                                                                                                                                                                                     
                                                                                                                                                                                                                                                               
    or with the pg_config option in 'setup.cfg'.                                                                                                                                                                                                               
                                                                                                                                                                                                                                                               
    If you prefer to avoid building psycopg2 from source, please install the PyPI                                                                                                                                                                              
    'psycopg2-binary' package instead.                                                                                                                                                                                                                         
                                                                                                                                                                                                                                                               
    For further information please check the 'doc/src/install.rst' file (also at                                                                                                                                                                               
    <https://www.psycopg.org/docs/install.html>).                                                                                                                                                                                                              
                                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                               
    ----------------------------------------                                                                                                                                                                                                                   
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-8rfmzv1e/psycopg2/

Add the following to the images:

RUN apt-get update --yes && \
    apt-get install --yes libpq-dev python3-dev