Allow imc-controller to list JobSinks

This is required otherwise MTChannelBasedBroker backed by IMC channel
can't forward events to JobSink. The error on ImMemoryChannel is
following:
```
failed to get lister for sinks.knative.dev/v1alpha1, Resource=jobsinks:
jobsinks.sinks.knative.dev is forbidden:
User "system:serviceaccount:knative-eventing:imc-controller" cannot list
resource "jobsinks" in API group "sinks.knative.dev" at the cluster
scope
```

config/channels/in-memory-channel/roles/controller-clusterrole.yaml

@@ -53,6 +53,15 @@ rules:
       - get
       - list
       - watch
+  - apiGroups:
+      - sinks.knative.dev
+    resources:
+      - jobsinks
+      - jobsinks/status
+    verbs:
+      - get
+      - list
+      - watch
   - apiGroups:
       - ""
     resources: