[JIRA] added new method get_issue_tree_recursive + docs + examples

[gkowalc]

I added a new method to the repo get_issue_tree_recursive which:

• method takes an issue key as input.
• Returns a list of dictionaries. Each dictionary represents a parent issue_key -> child_issue_key.
• Child_issue_key is either a subtask, or an inward link to another issue.
  I added warnings which specify limitations of the method - the user needs to have access to all linked issues and all linked * * issues must come from the same Jira instance (or from another instance if the user's API key also enables access to that instance).
• In addition to the method code, I have updated the docs and I have also added a sample use case.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 5.26316% with 18 lines in your changes are missing coverage. Please review.

Project coverage is 34.18%. Comparing base (978fa3f) to head (08d4acb).
Report is 1 commits behind head on master.

Files	Patch %	Lines
atlassian/jira.py	5.26%	18 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1352      +/-   ##
==========================================
- Coverage   34.25%   34.18%   -0.07%     
==========================================
  Files          46       46              
  Lines        8408     8427      +19     
  Branches     1178     1185       +7     
==========================================
+ Hits         2880     2881       +1     
- Misses       5413     5431      +18     
  Partials      115      115              

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[gonchik]

@gkowalc thanks