Add GitHub actions workflow to tag new releases from .github/piper-cut-cl.json

[lauraharker]

This workflow will run whenever a new commit is pushed to master.

If .github/piper-cut-cl.json is unchanged from the previous commit, this workflow does nothing.

Otherwise, the workflow finds the most recent commit prior to the new cut CL, and creates a new tag based on that commit.

Part of #4220.

For example, from my closure-compiler fork, here's:

• an action that created a new tag v12345 - https://github.com/lauraharker/closure-compiler/actions/runs/13511435580/job/37752293605
• an action that did basically nothing because piper-cut-cl.json was unchanged - https://github.com/lauraharker/closure-compiler/actions/runs/13511508884/job/37752492936

[lauraharker]

Alternatively we could find the version id from .github/piper-cut-cl.json & always check if that exists as a tag, anywhere -

I think the behavior should be equivalent when everything's working, but:

• this approach is slightly faster, since the step of fetching all known tags can take 20-30 seconds
• this approach would also skip more release tags if the CI were broken for other reasons, though - when the CI was fixed, we wouldn't go back and create a tag for the current .github/piper-cut-cl.json

[lauraharker]

@ChadKillingsworth FYI