Add verify command as described in RFC.

Add Admin rpc to verify plan application for concrete plan; any plan.
Verification uses two calls, one for single node checks and another for fanout to all cluster nodes using gossip info. Cluster check includes following checks: fanout to other nodes to check plan application status, decommission status of failed nodes, range availability check.

Add cli command that calls Admin rpc above and presents verification response to operator.

Part of #77273

Jira issue: CRDB-22131

Epic CRDB-14205