Change image registry from k8s.gcr.io to registry.k8s.io

https://groups.google.com/a/kubernetes.io/g/dev/c/DYZYNQ_A6_c

Author: Gabriel Mainberger

class/defaults.yml

@@ -7,5 +7,5 @@ parameters:
         version: '3.8.2'
     images:
       metrics_server:
-        image: k8s.gcr.io/metrics-server/metrics-server
+        image: registry.k8s.io/metrics-server/metrics-server
         tag: v0.6.1