Add code review checklists

[stephaniehobson]

One-line summary

Add code review checklists

Significant changes and points to review

The idea is to create a GitHub action which will post appropriate checklists in a comment when a pull request is opened if some file types have been touched. So, these are a little general in places. But, I'm hoping they can help keep our code base consistent-ish as we have more new developers contributing.

• Add checklists for:
  • General
  • HTML
  • CSS
  • JS
  • Media
  • Analytics
  • Experiments
  • Localization
  • Tests
• Some markdown clean up

Issue / Bugzilla link

n/a

Testing

[stevejalim]

IIRC we don't need to add the cli explicitly - the gh cli is available in all workflows run on github-hosted runners.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.90%. Comparing base (b0478b6) to head (9b97ec9).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16447      +/-   ##
==========================================
- Coverage   79.91%   79.90%   -0.01%     
==========================================
  Files         158      158              
  Lines        8538     8531       -7     
==========================================
- Hits         6823     6817       -6     
+ Misses       1715     1714       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

Thank you for your pull request. Based on the contents you may need to double-check these things:

No specific checklists needed for this PR.

[stevejalim]

Thank you for your pull request. Based on the contents you may need to double-check these things:

No specific checklists needed for this PR.

@stephaniehobson If the bot can determine that no checklists are available, can it also swap the first line of that message to just say "Thank you for your pull request. Based on the contents, there is nothing to double-check [beyond the usual diligent review]" or similar?

[stephaniehobson]

Superceded by #16460

[stephaniehobson]

@stevejalim I changed it to not comment if nothing is found.