Document changing service by changing the server name and services at the same time

This works fine if you 'rename' the node, i.e. change the name parameter of the server.

Re-opening this because I got caught out by this too (used the workaround in previous comment).

We should cover this (at least briefly) in the docs - https://github.com/couchbase/couchbase-operator/blob/master/docs/user/scalingCouchbase.md.