Add extra columns for EventListeners

Adds the address.url and the `Available` status as additional columns, so users
running `kubectl get` can access them easily.

Signed-off-by: Dibyo Mukherjee <dibyo@google.com>

config/300-eventlistener.yaml

@@ -42,3 +42,13 @@ spec:
   subresources:
     status: {}
   version: v1alpha1
+  additionalPrinterColumns:
+  - name: Address
+    type: string
+    JSONPath: .status.address.url
+  - name: Available
+    type: string
+    JSONPath: ".status.conditions[?(@.type=='Available')].status"
+  - name: Reason
+    type: string
+    JSONPath: ".status.conditions[?(@.type=='Available')].reason"