[BUG] Injected Broker relies on the default Channel provisioner

[grantr]

Describe the bug
The default Broker injected when a namespace is labeled with knative-eventing-injection=enabled has an empty channelTemplate value. When the template is empty, the Broker creates Channel objects which require an installed ClusterChannelProvisioner.

Expected behavior
ClusterChannelProvisioner is not used because it's deprecated.

To Reproduce

1. Find a namespace that has no default Broker.
2. Label the namespace with knative-eventing-injection=enabled
3. The Broker will create Channel objects.

Knative release version
0.7.1

Additional context
I think this means we can't remove CCPs in 0.8.

[grantr]

I think this means we can't remove CCPs in 0.8.

The simplest path forward might be to add the ability for Channel to choose a default CRD channel when provisioner is empty. Then the existing Channel object still works as expected. The only real difference from a user perspective is that there's an extra object (the CRD channel object).

Once that's done, we can keep the Channel object as the standard way to create a default channel, while also deprecating the provisioner field in 0.8.

[vaikas]

/assign @nachocano
I think with the default channel you added, this can be closed?

[nachocano]

/assign @nachocano
I think with the default channel you added, this can be closed?

Yes, this can be closed as per PR
Thanks!

/close

[knative-prow-robot]

@nachocano: Closing this issue.

Details

In response to this:

/assign @nachocano
I think with the default channel you added, this can be closed?

Yes, this can be closed as per PR
Thanks!

/close

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