[Fix #4673] Migrate EvalAI CI/CD Workflow to Github Actions

[Zahed-Riyaz]

This PR aims to :

• Completely migrate EvalAI's current CI/CD workflow from Travis CI to Github Actions.
• Setup CI checks for linting, migrations, and static type checks.
• Decommission .travis.yml and remove Travis-specific config/integration from the repository.
• Update documentation to reflect the CI migration : make changes in README.md and other files to reflect the changes made.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.70%. Comparing base (96968d6) to head (868def7).
Report is 1187 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4685      +/-   ##
==========================================
- Coverage   72.93%   69.70%   -3.23%     
==========================================
  Files          83       21      -62     
  Lines        5368     3608    -1760     
==========================================
- Hits         3915     2515    -1400     
+ Misses       1453     1093     -360     

see 73 files with indirect coverage changes

see 73 files with indirect coverage changes

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