CI workflow updates to copy notes from fork after merge

[svarlamov]

We'd love for more open source maintainers (ourselves included) to retain the Git AI notes that come in from forks. This would require updates to our CI actions to copy over the Git AI notes from forks after PRs are merged.

1. Reference the existing CI logic and templates in src/ci
2. Support forks in the existing squash/rebase logic (I believe that forks do not currently copy notes in these flows either)
3. For normal merges (merge commit instead of squash/rebase), detect when we're merging from a fork and copy notes for the commits that we're merging in.
4. Update CI templates (if necessary, probably not as the templates already trigger on merges)

[svarlamov]

Related to #334

[svarlamov]

Following up on our discord chat, @Ngineer101 is taking this on