Pass all initial options as envs included with envFrom #25

I'll just copy&paste our chat with Kirill Ilin (@sircthulhu)

kvaps:
I've got an idea, what if we move all four of these flags into a configMap included with envFrom?

• --initial-advertise-peer-urls
• --initial-cluster
• --initial-cluster-state
• --initial-cluster-token

It seems they are only relevant during initialization and might change over the lifetime of the cluster itself.

Kir:
We can remove them after the cluster is created :)

Except for the state.

kvaps:
Hold on, but what about adding new replicas and re-bootstrapping the old ones? How else will they know where to join?

With this approach, they will always have up-to-date information at startup.

Kir:
Overall, you're right :)

kvaps:
From the operator's side, we would only need to implement the deletion of old replicas.

Scaling up should handle itself.