Backport noxfile and other workflow changes

[gotmax23]

We should backport #314 and #258 that add the initial workflow automation after letting them sit on devel for a bit. We can also backport the requirements-relaxed change (#271). We should decide whether to create scheduled dependency updates for the stable branches or leave it to be done manually. I assume the manual approach is preferred.

[samccann]

Is this suggestion to backport only to stable-2.15 or all the way to stable-2.13?

[samccann]

As for scheduled dependency updates on stable branches - for non-latest I would definitely say no, we don't do it at all unless something has broken. Those are supposed to be 'bugfix/securityfix' releases so we should follow that approach even in docs imo.

For latest - my preference is 'if it ain't broke, don't fix it'. As in again, dependency updates on all stable branches should be limited to only what is required, not just what is desired. So unless we had a strong need, we woudln't update sphinx in a stable branch. We'd avoid updating antsibull-docs as well unless it was an agreed feature we wanted to add to the latest docs. Bugfixes for antsibull-docs would definitely get backported tho if that makes sense?

[gotmax23]

The stable-2.15 backport (#342) was merged earlier today. Thanks for reviewing, @oraNod. I'll open equivalent stable-2.14 and stable-2.13 PRs later.

[gotmax23]

stable-2.14: #685

[gotmax23]

Fixed in #685