Add plan stading as described in RFC.

Add Admin RPC to stage plan on all cluster nodes. Staging includes discovering all cluster nodes, verifying that there's no conflicting plan already staged and sending plan to every nodes. Every nodes then saves plan locally if there's any data in the plan eligible for application on that node, it also updated decommissioned status for nodes removed in local tombstone storage.

Extend apply-plan command to distribute plan in half-online mode.

Part of #77273

Jira issue: CRDB-22132

Epic CRDB-14205