List applying policies in Channel .status.policies and propagate applying EventPolicies to the underlying channel

[creydr]

As the Eventing Authorization feature track describes, target resources of EventPolicies, will reflect in their status, which EventPolicy is applied to them.

For example:

apiVersion: messaging.knative.dev/v1
kind: Channel
metadata:
  name: my-channel
spec:
  ...
status:
  ...
  policies:
    - name: event-policy
      apiVersion: v1alpha1
    - name: another-event-policy
      apiVersion: v1alpha1

  conditions:
    - type: Ready
      status: "True"
    - type: EventPoliciesReady
      status: "True"

As Channels should support EventPolicies, wee need to do the following:

• Update the Channel reconciler to list the applying policies in the Channels .status.policies and set the channels EventPoliciesReady condition. Also watch EventPolicies for changes.
• Set EventPoliciesReady condition to true, in case no policy applies, and set message according to the default-authorization-mode (e.g. Default authorization mode is 'allow-all'). Check the Default Authorization Mode section in the feature track for additional information.
• Copy the EventPolicies which apply for the Channel down to the underlying channel, so that EventPolicies which apply for the Channel also apply for the underlying channel.

Prerequisites:

• Add Library to support on AuthZ #7985
• Add AppliedEventPoliciesStatus type #7975