Add alert email to ci-etcd-k8s-coverage-amd64 job

Signed-off-by: Aleksander Mistewicz <[email protected]>

Author: AwesomePatrol

config/jobs/etcd/etcd-periodics.yaml

@@ -2143,6 +2143,8 @@ periodics:
     preset-dind-enabled: "true"
   annotations:
     testgrid-dashboards: sig-etcd-periodics
+    testgrid-alert-email: [email protected]
+    testgrid-num-failures-to-alert: "3"
   spec:
     volumes:
       - name: tmpdir