Add option to customize load balancer source ranges for pgbouncer, similar to https://docs.percona.com/percona-operator-for-mysql/pxc/operator.html#haproxy-loadbalancersourceranges and https://docs.percona.com/percona-operator-for-mongodb/operator.html#sharding-mongos-expose-loadbalancersourceranges

A similar option could also be added to expose the postgresql nodes although only the proxy is necessary for DBaaS.