Tracking issue for making region size dynamic

[bufferflies]

Enhancement Task

Summary:

ref: #tikv/tikv#11515
Make the size of a region dynamic, and only set a upper limit.
This is the first step that we try to support PB scale cluster.

Tasks：

• Opeator life cycle will adjust by region size not hard code includes expired、timeout、influence. related: Opeator life cycle will adjust by region size not hard code includes expired、timeout、influence #4456
• balance region scheduler will stready after new store joined includes. #4654
• checker will work well after one store offline.
• PD schedules well on both size balance and load balance.
• [Dynamic Region] TiKV/PD support Region Buckets  #4668
• PD uses buckets to do hotspot split and deprecated TiKV local hotspot split

[lhy1024]

TiKV/PD support processing flow report in a standalone stream.

Maybe we can use store heartbeat

[BusyJay]

Can these tasks be closed?

[bufferflies]

Can these tasks be closed?

yes ， closed by completed