implement keyspace management #5293
Description
Development Task
In order to let multiple keyspaces share the same PD cluster, PD needs to provide storage and ways to manage keyspace metadata.
Feature request: tikv/tikv#12998
Parent Issue: tikv/tikv#12999
Task List
- make id allocator more general purpose #5294
- keyspacepb pingcap/kvproto#952
- storage: keyspace management #5265
- server: keyspace management #5291
- client: keyspace client #5297
- kv: added RunInTransaction style transaction interface #5347
- Refactor keyspace manager using RunInTxn & Tombstone Keyspace
- keyspace: add region label when creating keyspace #5844
- keyspace: Pre alloc keyspace #5869
- apiv2: keyspace management #5313