[gha] add PR changelog check

[dsokal]

Why

This PR implements my idea on how to make skipping adding the changelog entry less likely.

How

• Add a workflow that fails if the PR didn't modify CHANGELOG.md.
• The check is skipped if "no changelog" label is added to the PR.
• Comment PR with the check status.

Test Plan

[github-actions]

Size Change: -424 B (0%)

Total Size: 40.9 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	40.9 MB	-424 B (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Merging #1798 (19e0f1d) into main (da4b56a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1798   +/-   ##
=======================================
  Coverage   52.11%   52.11%           
=======================================
  Files         472      472           
  Lines       16798    16798           
  Branches     3524     3524           
=======================================
  Hits         8753     8753           
  Misses       7380     7380           
  Partials      665      665           

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[github-actions]

⏩ The changelog entry check has been skipped since the "no changelog" label is present.