Initial API fields for HA control plane

**Problem**

Now that leader election has landed in 0.13, we should make the operator deploy an HA configuration by default.

**[Persona:](https://github.com/knative/eventing/blob/master/docs/personas.md)**

Users of the operator


**Exit Criteria**
A measurable (binary) test that would indicate that the problem has been resolved.

**Time Estimate (optional):**
Simple
