Overhaul the labels page to reflect current GH labeling practice

[ezio-melotti]

This PR updates the triage/labels.rst page, that contained outdated references to removed/renamed labels and previous fields used by bpo.

The PR is still a draft. The first commit documents the existing labels. Next, most of the remaining text in the page will either be deleted or moved to other sections, since it mostly covers bpo fields. Finally, I might add more links to the relevant sections to avoid duplicating information.

This is part of CPython labels and will fix the following issues:

Fixes#296
Fixes#518
Fixes#821
Fixes#868
Fixes#929

The structure and grouping of the labels is also based on python/core-workflow#450

[terryjreedy]

I don't see any mention of automerge in the patch, but see comment on #518.

[ezio-melotti]

I haven't used automerge myself so, even though I'm planning to document it, I first have to figure out how it works exactly, and when it should be used.

[ezio-melotti]

I updated the PR and marked it as "ready for review". It's still not perfect, but we can start merging this and apply further improvements in separate PRs. I left some inline comments to facilitate the review.

[CAM-Gerlach]

Thanks @ezio-melotti , this seems like a great set of major and well-needed improvements overall. I did have a number of specific suggestions for tweaks, most minor and a few less so, as well as a handful of broader comments and questions. Thanks!

[hugovk]

Thank you for this!

Some suggestions mostly about preserving #anchors where appropriate.

[hugovk]

This PR could also close #296.

[CAM-Gerlach]

It wouldn't let me add that one under Development for whatever reason, so I edited the OP directly (and made the others proper fix-tagged). I also fixed the title to be more useful/descriptive and less generic; refine it further as desired, of course.

[hugovk]

🏷️ Thank you!

[CAM-Gerlach]

I had a handful of final followups, ref target label tweaks and a few other fixes I spotted—all as one-click apply able suggestions—plus re-iterating one previous unresolved comment requesting reverting the "assignee" section removal that has no existing replacement, and should be iterated on in the future. Other than that, LGTM, and I resolved the other outstanding comments (aside from a couple addressed here). Thanks @ezio-melotti for all your hard work (and patience) here!

[CAM-Gerlach]

A few final followup fixes and one minor thing I couldn't reach (that may be out of scope), otherwise LGTM, thanks! Marked everything else as resolved now.