Add GitHub Actions configuration

[cottsay]

This will make it more simple to invoke the action with something like:

  steps:
    ...
    - uses: ros-infrastructure/rosdistro-reviewer@main
      with:
        token: ${{ github.token }}
    ...

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.74%. Comparing base (6892b82) to head (5a1a1c8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #8   +/-   ##
=======================================
  Coverage   55.74%   55.74%           
=======================================
  Files          11       11           
  Lines         409      409           
  Branches       95       95           
=======================================
  Hits          228      228           
  Misses        176      176           
  Partials        5        5           

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