Add implementation of collection rpc in Admin as per RFC:

Collection should do a best effort collection of range descriptor metadata about all ranges. This full or partial info should be streamed back to caller.
Collection should use fanout to nodes discovered via gossip to collect replica info and stream info back to caller.
It should tolerate any partial failures and send only available info.

Depends on changes to plan protobuf definition in #93037

Part of #77273

Jira issue: CRDB-22129

Epic CRDB-14205