[FEATURE] Support PostgreSQL as DB backend

[imyousuf]

Is your feature request related to a problem? Please describe.
Not specifically related to a problem; but from various performance comparison it seems for write heavy load PostgreSQL is better suited.

Describe the solution you'd like
The application supports both MySQL and PostgreSQL as DB backend.

Describe alternatives you've considered
We want to remain in the realm of RDBMS still so not much open source alternate available.

Additional context
Supporting PostgreSQL also opens up the possibility of using CockroachDB.