Automate generation of lists of build options for different ROOT versions

[eguiraud]

install/build_from_source.md includes the build options for the latest release. @hageboeck has a script that automatically generates the markdown table with the options, and we could automatically re-generate it as needed as a github action.

We could/should also produce such tables for other ROOT releases and link to them from somewhere visible.

[hageboeck]

It should boil down to something like

1. Inside the root directory of the website project, run bash .github/scripts/generateBuildOptions.sh <branch> [branches ...].
   This will put the markdown tables for all branches where the config could be retrieved successfully into _include. (Or it will just update the existing files. On failure, existing files remain unchanged.)

2. Link the latest available branch to something like _include/build_options_latest.md, so the "main" build options website doesn't have to be edited all the time.

3. Generate other websites that link to previous versions.

[eguiraud]

on second thought I will take care of this one