Implement Flow Controller

[vaikas]

Expected Behavior

When creating Flow Resource, the controller will then:

1. Resolve the target of the action [say, Route / Service from serving stack] using dynamic k8s client, so no compile / runtime dependency on the serving stack. Note that in order for this to work correctly, Route / Service will need to expose a k8s service in its Status field in addition to todays Domain.
   2.. Create a Channel on the "Default Bus" [should come from a ConfigMap]
   3 Create a Subscription on the created channel in step 2 to the target of resolved target in step 1.
2. Create a Feed targeting the Channel created in step 2

This is roughly the steps. This will need to be documented obviously more thoroughly.

Actual Behavior

There's no controller.