Add startup probe for controller (#1063)

When there are many Kingress is deployed on the system, it takes long
time to start net-kourier-controller (e.g. 12 minutes for 1000 ksvc)
and Liveness/Readiness probe fails.

We should improve the process but for now we add a startup probe for
to avoid the Liveness/Readiness probe failure.

config/300-controller.yaml

@@ -63,6 +63,11 @@ spec:
           - name: http2-xds
             containerPort: 18000
             protocol: TCP
+          startupProbe:
+            grpc:
+              port: 18000
+            periodSeconds: 10
+            failureThreshold: 120
           readinessProbe:
             grpc:
               port: 18000