Cloud Build: Add missing config, remove unused ones. (#11777)

Co-authored-by: Marco Ebert <[email protected]>

Author: k8s-infra-cherrypick-robot

images/ext-auth-example-authsvc/cloudbuild.yaml renamed to images/e2e-test-echo/cloudbuild.yaml

@@ -8,4 +8,4 @@ steps:
     entrypoint: bash
     args:
       - -c
-      - gcloud auth configure-docker && cd images && make NAME=ext-auth-example-authsvc push
+      - gcloud auth configure-docker && cd images && make NAME=e2e-test-echo push