Improve frontend login redirections

I figured it's best to create a new setting for that and implemented this.
I also improved in-code comments for the existing options, such that there is a better overview of what they actually do. During implementing I realized we need to keep paths, not routes. Since in the path processor, the route name is not available.

The MR adds /user to and the user account page to the "keep frontend" paths, that way a user login in the frontend keeps you in the frontend.

unfortunately the gitpod link does not work for lupus-decoupled branches still, see https://www.drupal.org/project/lupus_decoupled/issues/3347260#comment-15... 🐛 Gitpod branch checkouts always use 1.x-dev Active

anyway, I checked the code out manually there and tested it at the gitpod environment also. works as it should!

re-checking on the solution, I think this is the right way and solves the issue. thus, moving on - merged!

Automatically closed - issue fixed for 2 weeks with no activity.