redpanda: Allow rpc advertised address to be overridden and templated

[chrisseto]

One of the use cases for extraInitContainers is attempts to modify the redpanda.yml. This isn't likely to work particularly well for a variety of reasons most importantly, we're hoping to do away with the extra___ attributes in the long run.

@vuldin is experimenting with stretch clusters and needs to be able to customize the advertised address of the RPC listener. We should just add support for modifying it in the same way that we allow customizing Kafka's RPC advertised addresses.

JIRA Link: K8S-297