Use statefulset for cluster.

[thedodd]

I got started with the nats-operator helm chart. Everything works well there. As far as the streaming operator:

• it would probably be best to use statefulsets for the actual cluster itself, as this will support volume claims much better. Otherwise, seems like you can only use a single node when running with DB or volume persistence.
• would be awesome to turn this into its own helm chart as well, as that would definitely help with parameterization and other such issues (which I believe are still in the TODO.md in this repo).

Thanks for all the excellent work so far!!!

[wallyqs]

Thanks for the feedback! For now here is a helm chart that doesn't use the nats streaming operator and uses instead a statefulset here if want to take a look: https://github.com/wallyqs/nats-streaming-cluster-chart