Document `listenerClass` usage in operators or global concepts page

[maltesander]

We currently do not document properly how our services are created.

After stackabletech/issues#360 we do not create NodePorts per default, this changes the way users interacted with our products (you explicitly have to set the listenerClass if you want a NodePort).

This should be fixed in each operator, or a global concepts page should be created and linked to in each operator.

• global concepts page updated: Updated text for service exposition #446

### Tasks
- [x] Add docs for `listenerClass` in each operator
- [x] Fix comment in CRD to proper english
- [x] Adapt getting started guides and (if available) examples with `listenerClass` Nodeports

### Operators
- [ ] https://github.com/stackabletech/airflow-operator/pull/320
- [ ] https://github.com/stackabletech/druid-operator/pull/466
- [ ] https://github.com/stackabletech/hbase-operator/pull/390
- [ ] https://github.com/stackabletech/hdfs-operator/pull/387
- [ ] https://github.com/stackabletech/hive-operator/pull/367
- [x] Kafka -> Not configurable, only nodePort supported
- [ ] https://github.com/stackabletech/opa-operator/pull/471
- [ ] https://github.com/stackabletech/nifi-operator/pull/500
- [ ] https://github.com/stackabletech/spark-k8s-operator/pull/276
- [ ] https://github.com/stackabletech/superset-operator/pull/399
- [ ] https://github.com/stackabletech/trino-operator/pull/465
- [ ] https://github.com/stackabletech/zookeeper-operator/pull/721

[lfrancke]

While we're at it we should look at the CRD level docs for the listenerClass as well as that doesn't seem to be entirely proper english.

[maltesander]

We should add the listenerClass: external-unstable in all getting started guides and examples as well. Otherwise you might install it but are not able to interact with the UI.

[lfrancke]

Maybe already done: https://docs.stackable.tech/home/stable/concepts/service-exposition.html
Check during refinement