preset flag as combination of theme and builder

[epogrebnyak]

Currently preset flag seems a combination of builders and themes - if there is both -t | --theme and -b | --builder flag, then presets can be defined in their terms: -p rtd is -t rtd -b html and -p xml is -b xml

  -p, --preset [xml|latex|dirhtml|alabaster|rtd|furo|pydata|vitepress]
                                  Documentation preset.

Users for quickstart could use -p and later refine their pipelines with -t / -b.