Add github action for rebasing PRs

[gregjopa]

This github action adds support for commenting "/rebase" on a PR to trigger a rebase. https://github.com/marketplace/actions/automatic-rebase

[codecov]

Codecov Report

Merging #1495 (47d5ad0) into master (9daaf38) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1495   +/-   ##
=======================================
  Coverage   50.75%   50.75%           
=======================================
  Files          83       83           
  Lines         930      930           
  Branches      157      157           
=======================================
  Hits          472      472           
  Misses        397      397           
  Partials       61       61           

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[gregjopa]

I'm going to close this unmerged. These two issues are blockers in my opinion:

• Keep original committer cirrus-actions/rebase#33
• Rebase command can not trigger test check workflow cirrus-actions/rebase#65