Conversion, store and serving of v1beta1 APIs

[nachocano]

Problem
Once we have the v1beta1 APIs #614, we need to add the proper conversion mechanism, and start serving them.

Persona:
Developer

Exit Criteria
Serving v1beta1 APIs and provide conversions if needed

Additional context (optional)
knative/eventing#2508

[nachocano]

When we start serving v1beta1, I think we will break gcloud integration.
We should make sure we are not. We should have the gcloud E2E tests in place before doing so.
#556

[nachocano]

my apologies, I was too optimistic, won't be able to make this in the three days I have remaining.
/unassign