Update to slf4j 2.0

[patriknw]

Sl4fj 2.0 is not fully backwards compatible. We made a workaround in #31825 to make it work with both. We have been holding back to update the dependency to 2.0 so that Akka wouldn't enforce all downstream projects to bump to later slf4j.

Sooner or later we will have to update, but no decision on when we will do that yet. Important that we make that change in all Akka projects at the same time to avoid confusion.

We have already seen that 2.0 is brought in by transitive dependencies of external libraries. akka-persistence-jdbc and the Slick dependency is one such, and we pinned slf4j to 1.7.36. Remember to remove that when we update.

[patriknw]

another pin in Akka Projections due to the Slick dependency

[johanandren]

And one more in akka-persistence-r2dbc (only migration tool tests though)