Switch default branch to to Drupal 11

[AlexSkrypnyk]

With Drupal 11 is now available for several months, I think we need to switch the default branch to D11 and update docs.

I do not have permissions to do so - maybe you have @leymannx or @webflo

[normanlolx]

I also can't. @webflo you turn. 🙏🏻