Review merging of config/listener-class info

[adwk67]

This issue arises from stackabletech/airflow-operator#604
Specifically, the points we want to re-visit are:

• possibly have an unversioned variant of build_recommended_labels in operator-rs (see comment)
• correlate group listener name and role-dependent listener-class, so that the main merged_config can be used (see comment and comment and comment), considering what can be moved into operator-rs

[NickLarsenNZ]

Maybe this can be moved into stackabletech/issues, because it will affect other operators too.

I am hitting this the zookeeper-operator.