Document the serviceName feature

[pebrc]

The service name feature introduced in #4404 is currently only documented in our CRD API docs. We should mention it in the product documentation. We should also call out that if users chose to customise the service and chose to override the default port declaration they need to use either "https" for TLS secured connections or "http" for unencrypted connections.

[pebrc]

This is actually already documented in the advanced section under "traffic splitting" (and mentioned in a few other places) so I am closing this issue.