CRD docs: polish epic

[fhennig]

The initial work to get generated docs up and running was done: #328

Now we need to fill the docs with content.

And then we need to update the CRD docs for all operators, similar to the druid PR:

### Operators
- [ ] https://github.com/stackabletech/airflow-operator/pull/354/
- [ ] https://github.com/stackabletech/druid-operator/pull/494
- [ ] https://github.com/stackabletech/hbase-operator/pull/425
- [ ] https://github.com/stackabletech/hdfs-operator/pull/433
- [ ] https://github.com/stackabletech/hive-operator/pull/394
- [ ] https://github.com/stackabletech/kafka-operator/pull/645
- [ ] https://github.com/stackabletech/nifi-operator/pull/537
- [ ] https://github.com/stackabletech/spark-k8s-operator/pull/319
- [ ] https://github.com/stackabletech/superset-operator/pull/431
- [ ] https://github.com/stackabletech/trino-operator/pull/510
- [ ] https://github.com/stackabletech/zookeeper-operator/pull/749
- [ ] https://github.com/stackabletech/commons-operator/pull/190
- [ ] https://github.com/stackabletech/secret-operator/pull/333
- [ ] https://github.com/stackabletech/listener-operator/pull/123

There is a style guide here: https://docs.stackable.tech/home/nightly/contributor/style-guide#_crd_documentation

Also, all the CRD docs should be linked under "Reference" in our regular docs.

### Products
- [ ] https://github.com/stackabletech/documentation/pull/509
- [ ] https://github.com/stackabletech/airflow-operator/pull/360
- [ ] https://github.com/stackabletech/druid-operator/pull/500
- [ ] https://github.com/stackabletech/hbase-operator/pull/433
- [ ] https://github.com/stackabletech/hdfs-operator/pull/446
- [ ] https://github.com/stackabletech/hive-operator/pull/398
- [ ] https://github.com/stackabletech/kafka-operator/pull/650
- [ ] https://github.com/stackabletech/nifi-operator/pull/546
- [ ] https://github.com/stackabletech/spark-k8s-operator/pull/332
- [ ] https://github.com/stackabletech/superset-operator/pull/438
- [ ] https://github.com/stackabletech/trino-operator/pull/516
- [ ] https://github.com/stackabletech/zookeeper-operator/pull/754
- [ ] https://github.com/stackabletech/commons-operator/pull/192
- [ ] https://github.com/stackabletech/listener-operator/pull/130
- [ ] https://github.com/stackabletech/opa-operator/pull/499
- [ ] https://github.com/stackabletech/secret-operator/pull/338

also this: stackabletech/crddocs#7

also this: #510

[adwk67]

stackablectl now uses -c kind instead of -k to create a kind cluster inline, and the cluster is a single node one. The getting started guides still refer to -k in some places.