chore: add backport github action

[carolinaecalderon]

Ticket

CM-446

Description

See https://hpe-aiatscale.atlassian.net/wiki/x/CgBLZQ for more details.
Suppose a developer wants to backport a fix XYZ into release branch release-A. On the pull request for XYZ, add labels backport release-A. Then, after the PR is merged, the github action will trigger :
(1) creating a new backport PR from main into the release branch (in this case release-A)
(2) automatically merging the backport PR

Test Plan

Manual testing done on https://github.com/carolinaecalderon/github-backport

Checklist

• Changes have been manually QA'd
• New features have been approved by the corresponding PM
• User-facing API changes have the "User-facing API Change" label
• Release notes have been added as a separate file under docs/release-notes/
  See Release Note for details.
• Licenses have been included for new code which was copied and/or modified from any external code

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[mackrorysd]

My comment aside, I think this is looking good. I'm not familiar with Github Actions though, so we ought to have a second set of eyes besides me.

[mackrorysd]

Doesn't this comment belong a few lines lower?

[carolinaecalderon]

This section was copy/paste'd from https://github.com/tibdex/backport/blob/main/.github/workflows/backport.yml, but I can move the comment around