Fix the Moore CI docs pipeline

Cherry-picked the relevant commits from !3422 (merged) as requested by @jonrob.

With help from @jonrob and @clemenci, I've modified the .gitlab-ci.yml configuration so that the pipeline can work out what branch is being targeted and also to which nightly build slot that would correspond.

The latter should fix the docs again and keep them alive on all protected branches (they were hard-coded to look at lhcb-master, but of course we're working on 2024-patches and the two have diverged).

The former should speed up the formatting check, as currently it is checking every file that differs between the branch and master for correct formatting - now it should just check only those that differ w.r.t the given target branch.

added Documentation bug fix labels

requested review from @jonrob

assigned to @rjhunter

changed title from Fix the Moore CI pipeline to Fix the Moore CI docs pipeline

Hello @jonrob, Marco is on holiday but he kindly gave me some pointers to streamline the logic to work out the target branch on-the-fly. I've cherry-picked the relevant commits here from !3422 (merged) as you asked. The CI pipeline there is already happy, so I assume this one will be OK as well. If so, would you be happy to merge it or do you have some more thoughts on it? Cheers.

added RTA label

mentioned in merge request !3422 (merged)

Hello @rjhunter, as you know from recent exchanges, we have a similar issue in DaVinci that the docs are rendered on the site only for master. That ought to be fixed soon so that the most up-to-date and relevant for 2024 documentation is made available online to users. I do not ask you to adapt/amend DaVinci - though you're most welcome! - but let me here ping @masmith so that the issue gets better on the radar.

There is also a related matter that I would like to see discussed more widely at some point, which is the fact that our Sphinx docs (here talking for all we have, project agnostic) by design show the latest/HEAD and we cannot consult what was the status or what was available for a given version. In some non-LHCb projects I've seen people use ReadTheDocs to have the tag-specific versions available, keeping the latest and greatest as the "master project docs" (sometimes even in a project specific site and not ReadTheDocs). We could envisage something along such a route and that requires some exchanges among a few of us. Now you know :-). Feel free to resolve this as a follow-up. I wanted to "dump" this info as it's been in my mind for a while.

FYI @nskidmor, @decianm and @cmarinbe, @vaneldik, @mwhitehe.

requested review from @msaur

removed review request for @jonrob

resolved all threads

approved this merge request

merged

mentioned in commit 7bc9d922

mentioned in merge request !3378 (merged)