Feature enhancements

• Speed up the exit process of schedulers #4146

Bug fixes

• Fix a bug that the schedule generated by the region scatterer might decrease the number of peers #4565
• Fix the issue that Region statistics are not affected by flow-round-by-digit #4295
• Fix slow leader election caused by stucked region syncer #3936
• Support that the evict leader scheduler can schedule regions with unhealthy peers #4093
• Fix the issue that the cold hotspot data cannot be deleted from the hotspot statistics #4390
• Fix a panic issue that occurs after the TiKV node is removed #4344
• Fix the issue that the scheduling operator cannot fail fast because the target store is down #3353