Reorganize makefiles and roll out consistent debug structure to them

What does this MR do and why?

Continuing on creating consistent debug output, this MR:

• Reorganizes Makefiles so that there is a "common" file where we can put variables used in other places.
• Introduces the support directory, very much like gitlab-development-kit (https://gitlab.com/gitlab-org/gitlab-development-kit/-/tree/main/support) where non-core things can be placed to get them out of the root directory. I think we'd move scripts in there too.
• Make printf debug output look indistinguishable from gum debug output for places where we can't be sure we have gum.
• Make sure that all Make targets have consistent debug output.

How to set up and validate locally

1. Configure a local GitLab Docs environment.
2. Check out this branch.
3. Run make setup and see that printf Make targets look gum-like.
4. Run make test and see where some lines are completely colorized (like a "heading") and other lines only have the debug level colorized. This is similar to how make update-all-projects looks.

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.