Experiment with speeding up the repair

[Michal-Leszczynski]

We are aware that SM 3.2 repair changes improved stability, but also slowed down the repair. For some use cases it's good, but sometimes it is rough when the repair works for many days (see https://github.com/scylladb/scylla-enterprise/issues/4006). Introducing small table optimization (#3642) will surely help, but it won't solve the entire problem. I see two possible improvements:

Tasks

Beta Give feedback

1. Coalesce token ranges sent in repair jobs #3789
   enhancement repair +2
   
2. Optionally allow many repair jobs per host #3790
   enhancement repair +2

Both of them are actually rather small changes on SM side. The bigger problem could be with testing - this would require QA assistance.
None of those improvements would be used by default - they could be optionally turned on by proper SM flags or config.

@karol-kokoszka @vladzcloudius @asias I know that you have been discussing similar topics on various issues, but I would like this task list to summarize your opinions.
FYI @tzach