Add field to store github_branch for challenges

[Zahed-Riyaz]

This PR amends #4737 to store github_branch field for challenge creation.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.91%. Comparing base (96968d6) to head (c8bd7c9). Report is 1222 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4745      +/-   ##
==========================================
+ Coverage   72.93%   76.91%   +3.98%     
==========================================
  Files          83       21      -62     
  Lines        5368     3608    -1760     
==========================================
- Hits         3915     2775    -1140     
+ Misses       1453      833     -620     

see 75 files with indirect coverage changes

see 75 files with indirect coverage changes

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[Zahed-Riyaz]

The migration as of now adds challenge_github_repo_branch_partial_idx which ensures that challenges are unique to the repository's branch, i.e, validating that the combination of branch and repo is unique to a challenge and can't be used to create multiple challenges.

This is why changes were made in test_views.py. To ensure each challenge has a unique name, the following change was made : challenge <-> challenge1 in the GetChallengeBasedonTeams set up.