Refactor the GitHub Workflows in this package

[jcfreeman2]

There's an awful lot of code in our Workflows which is basically repeated. For one thing, we have six different files for six different ways of cutting a release (nightly + candidate + frozen) * (sl7 + alma9), and they have lots of lots of stuff in common. It would be good to try to put a lot of this common code into scripts, since (1) it would just be good coding practice to support the DRY principle, and (2) scripts would allow us to recreate these Workflows on local hosts where we can poke around if something goes wrong, rather than being walled off by a GitHub Action.

[jcfreeman2]

Closing this Issue now that the refactor has been merged. A couple of things:

• Most of the refactor involved moving common functionality into .github/workflows/wf-setup-tools.sh and scripts/spack/build-release.sh. The latter, in particular, can be used at the command line to manually recreate a GitHub Action
• This refactor meant that the five release build Workflow files we have (nightly Alma9/SL7, frozen Alma9/SL7, and candidate Alma9 - yes, we don't have a candidate SL7 on the develop branch) reduced from 2327 to 1264 lines, or just over half the original length
• The refactor also included dropping the obsolete feature branch workflow dunedaq-feature-branch-cpp-ci.yml and regularizing the name of the nightly SL7 build (nightly-spack.yml -> nightly-spack-sl7.yml)

There absolutely are other improvements to be made. But the changes which got merged in are a major step in the right direction.