CustomBuild Server

[Hwurzburg]

The Custom Build server is being relied upon more and more by users, especially since we continue to remove features from boards even more frequently.

The present build_options.py has many bugs, with whole groups (like airspeed drivers) being non-functional....and there is no maintainer for this important ArduPilot feature....

at a minimum we need:

• CI testing of additions to build_options.py to assure that they actually work before merging new build_options.py changes
• a means to test locally....the current instructions do not work and produce errors when trying to check it locally....both because of changes in the python file and because the custom.ardupilot.org server runs stable and forks only replicate main (should be called master branch also) not the other branches!....also the setup for main checks needs an entirely different set of instructions since branch folders are involved
• a Maintainer for this repo.....Michelle is being overwhelmed and did not sign up as the Maintainer in any case...