More control over configuration of allowed blocks

Wow this is great work!

I think this can in theory be split into 2 different issues:

One for the alter hook, and the other for the "per nid" part

If we can get a merge request for this one in that would make it much easier to review, test and commit. Plus, if someone wants to create a separate issue for the alter hook, that seems even easier to add.

Ideally we should also add some tests for this, but let's start with addressing the above points?

Let me work on the "per nid" part and created a new ticket https://www.drupal.org/project/gutenberg/issues/3401847 ✨ Create a hook that allows to change the list of "*_allowed_drupal_blocks" Active for alter hook

I have updated the open MR !60 to include the alter hooks from patches #4&5.

Took the opportunity to make some changes regarding some Dependency Injections missing.
Good work 😉