Support PGBOUNCER deployment

[sbernauer]

Reported in https://stackable-workspace.slack.com/archives/C06H1D6FCJD/p1717413781794189

Relevant airflow helm-chart docs and config. The helm-chart creates a dedicated Deployment + Service.

In case we implement this we can e.g. either introduce a PgBouncerCluster CRD or offer this functionality on the AirflowCluster, in that case we should create the actual Deployment in operator-rs, so it can be re-used by other operators.

One possible outcome could be that we are not going to write an operator for pgbouncer and recommend an Open Source one instead