Repair of the SystemDistributed keyspace creates a non-trivial amount of memory pressure

When a repair without any particular option is triggered, the SystemDistributed keyspace is repaired for all range, and in particular the repair_history table. For every range, that table is written and flushed (as part of normal repair), meaning that every range triggers the creation of a new 1MB slab region (this also triggers quite a few compactions that also write and flush compaction_progress at every start and end).

I don't know how much of a big deal this will be in practice, but I wonder if it's really useful to repair the repair_* tables by default so maybe we could exclude the SystemDistributed keyspace from default repairs and only repair it if asked explicitly?