Introduce the Readonly flag in TableRouteValue

[WenyXu]

What type of enhancement is this?

Refactor, Tech debt reduction

What does the enhancement do?

We must set the read-only flag before actions for any dead or unavailable writable region(the Leader Peer).

We currently use the InactiveRegionManager. After the old MetaServer Leader crashes, the new Leader will re-register the inactive region. However, there may be a Datanode restart and get the wrong leases before the new Leader re-registering the inactive region.

Implementation challenges

No response

[WenyXu]

BTW, We might also need to introduce an Initializing flag for the writable region(the Leader Peer) to help MetaServer handle the region lease properly.