Create initial reconciliation workflow based on ahrtr/etcd-operator

[ahrtr]

Refer to the high level workflow.

There is a PoC ahrtr/etcd-operator, which already implements the reconciliation workflow, although some details are marked as TODO.

As the very first step, let's implement the reconciliation workflow based on ahrtr/etcd-operator/controller.go#L236. Once it's done, then users should be able to create an etcd cluster of any number of members (no TLS yet).

[nayihz]

If possible, I'd like to give it a try.