Enable LeaderCachedKvStore for meta server

[WenyXu]

What type of enhancement is this?

Performance, Refactor, Tech debt reduction

What does the enhancement do?

The meta server needs a cheap way to ensure the Datanode servers hold the correct Writable Region and Read-only Region. Due to all metadata mutation should be executed via meta server leader in distribution mode, we can utilize this character to cache all metadata in the meta server's memory.

Steps

Reclaim Mutation permissions

• Introduce the ReadonlyKvBackend for Frontend and Datanode.
• Execute create database in procedure #2601

Enable LeaderCachedKvStore

• Add initializing stage for caching key-value
• Reject requests during the initializing stage

Implementation challenges

No response