Add Redis support

It would make more sense to keep the solution and the background together over in ✨ Support external Flood Postponed: needs info , marking this as a duplicate. The code to add Redis (or whatever replaces it) is mostly complete in that issue, it just needs to be merged into the new layout. The code in the patches for FloodUnblockManagerBase in ✨ Make FloodUnblockManager generic Active seem to be based off the original issue. There are a pile of people who deserve credit for getting it to this point, plus more people who would be notified of the updates and changes in plan. I only ran into this due to the posts by Anybody and catch on that issue.

I announced splitting this issue in this comment:
https://www.drupal.org/project/flood_control/issues/2928007#comment-1553... ✨ Support external Flood Postponed: needs info

I would prefer to keep this in a separate issue, to keep the conversation focused on a smaller topic and make it easier to review.

I ll try to ensure that people are being credited and notified.