feat: PRs are added to repo-specific projects

[nedbat]

@feanil I need to write some docs, but the mechanisms and tests are here if you want to get a look.
@feanil This is ready for review.

Things I don't like about this:

• I don't know if this will even work for the "pull request from fork" case, because I think the API still won't let you add an item from own organization (or owner) to another organization. We need to test this.
  • Tested: pull requests from forks are PRs in the original repo, so this will work.
• It only does pull requests, not issues, because the bot currently only looks at pull requests. The shared action can do issues, but now we have two completely different mechanisms and configurations for issues vs pull requests.
• glom and backstage don't get along because backstage requires a key of "openedx.org", but then glom can't parse it as "metadata.annotations.openedx.org/add-to-projects", because glom splits on dots.

[codecov]

Codecov Report

Base: 89.14% // Head: 89.22% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (f5801f0) compared to base (cd733de).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   89.14%   89.22%   +0.07%     
==========================================
  Files          77       77              
  Lines        4571     4603      +32     
  Branches      473      477       +4     
==========================================
+ Hits         4075     4107      +32     
  Misses        459      459              
  Partials       37       37              

Impacted Files	Coverage Δ
openedx_webhooks/tasks/github_work.py	100.00% <ø> (ø)
openedx_webhooks/gh_projects.py	100.00% <100.00%> (ø)
openedx_webhooks/info.py	97.82% <100.00%> (+0.28%)	⬆️
openedx_webhooks/tasks/pr_tracking.py	97.13% <100.00%> (ø)
tests/conftest.py	97.89% <100.00%> (+0.09%)	⬆️
tests/test_data.py	100.00% <100.00%> (ø)
tests/test_faker.py	100.00% <100.00%> (ø)
tests/test_pull_request_opened.py	100.00% <100.00%> (ø)

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