MM-35518 - Add CodeQL check

[srkgupta]

Summary

Added step to run automated CodeQL checks. Once this file is merged, the codeql checks (code scanning checks) will automatically be performed on following conditions:

• new pull requests to master branch
• scheduled to run every week once (it automatically pulls the latest codeql checks added, if any)

Ticket Link

Fixes https://mattermost.atlassian.net/browse/MM-35518

[codecov-commenter]

Codecov Report

Merging #162 (9ba5253) into master (a868350) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #162   +/-   ##
=======================================
  Coverage   40.03%   40.03%           
=======================================
  Files           6        6           
  Lines         602      602           
=======================================
  Hits          241      241           
  Misses        345      345           
  Partials       16       16           

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[hanzei]

Please see my comment at mattermost/mattermost-plugin-github#442 (review)