Project management: automate adding package-related labels to PRs

[priethor]

What?

This PR automates adding package-related labels to PRs when they affect one or more npm packages. Related discussions in #52583 and #52727 (comment)

Why?

Labeling in detail is a burden, and often PRs get merged without many labels. Some labels can be automated, like package labels and many feature-related ones.

How?

By adding a labeler GitHub action that checks the path of the files affected by the PRs.

Testing Instructions

I've created a PoC in a test repository, and it seems to work fine!

[priethor]

Some packages don't have an associated label. This is direct to solve, and labels should be created later for these packages, but I didn't want to interfere with the WIP audit in #52583.

[github-actions]

Flaky tests detected in 9973baa.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/5587437804
📝 Reported issues:

• [Flaky Test] zoom animation #52381 in /test/e2e/specs/editor/blocks/image.spec.js

[jordesign]

It's beyond my skillset to comment on the code itself - but in terms of the labels being added it looks good to me

[priethor]

Thanks for taking a look, @jordesign . There are some label mismatches between the current labels and packages, as I noted in the spreadsheet from #52583. Since package labels should be a direct 1:1 mapping, I will move forward to updating them if you don't mind.

[apeatling]

This looks great, and should help the problem quite a bit. Looks thorough to me but I will hold off on approval until you have the label mismatches sorted.

[afercia]

Slightly unrelated and maybe it would have been better addressed in the contrext of #52583

I just noticed that there's no label for the existing package @wordpress/customize-widgets.
I'm not sure what the state of this package is, but it seems to me the lack of a label is inconsistent with the similar package @wordpress/edit-widgets which does have its own label: [Package] Edit Widgets.

Actual use case: I'd need the missing label to be added to #54148