Tag the very start of every new release branch

[bryevdv]

Currently, until there is a tag on a new release branch, e.g. branch-3.2 you see dev versions the reference the previous release:

Bokeh version       :  3.1.0rc1+49.g67e2eba9

I'd like to propose that the start of every new branch-x.y release branch be immediately tagged as a matter of policy. We could use something like 3.2.0.dev0, since we usually start actual dev releases with dev1, or maybe there is something else? As long as it sorts before "dev" versions I think anything sensible is OK. With a manual local tag as a test, we get a more accurate and useful version:

Bokeh version       :  3.2.0.dev0+10.g67e2eba9

It would be nice if we could just automate this as part of release machinery, but I don't think that is feasible since we usually create a new release level branch ahead of the next release. However, we probably could make a GH action for creating new release level branches, instead of doing it manually. A GH could take care of the tagging, making sure the version makes senses, etc. I would be 👍 since it would help anyone be able to correctly create a new release level branch, rather than just a few people who know the correct magic incantations to get it right.

As an aside: I also wonder if doing this would solve the "0.0.1" issue without requiring everyone to fork with full history? I think the setuptools SCM tool just needs some tag, and perhaps the new GH default fork would at least preserve tags on the default branch? (unclear, but it would be nice if so)

cc @bokeh/dev

[mattpap]

This has been bothering me as well for a few recent releases.

We could use something like 3.2.0.dev0 (...)

This seems reasonable to me.

[tcmetzger]

+1 from me, that sounds great! Automating this with a GH Action would be very helpful, to make sure this always works in a consistent and reliable way!