Document the operational procedure of renaming etcd cluster members

Follow-up task from this discussion: https://github.com/etcd-io/etcd/discussions/16403

We have existing documentation about adding/removing cluster members, and fundamentally renaming a node seems to require following this process, however we don't really talk about it anywhere. Leading to discussion questions like the one linked above.

We should consider updating either our operations guide or frequently asked questions (or both) to clarify that renaming a node follows the member remove and re-add process, as outlined in the linked discussion.