Assure periodic-weekly emails to zuul-jobs-failures

Assure periodic-weekly failures are sent to the new mailing list
creating for monitoring them.

Depends-On: https://review.opendev.org/#/c/748688/
Change-Id: I6a08d18f4a0973f67a6d5c3169f96dccd59edf8e

zuul.d/pipelines.yaml

@@ -144,6 +144,26 @@
     failure:
       mysql:
 
+- pipeline:
+    name: periodic-weekly
+    post-review: true
+    description: Jobs in this queue are triggered on a weekly timer.
+    manager: independent
+    precedence: low
+    trigger:
+      timer:
+        # Saturday 8am UTC is a better time to start weekend jobs, as Sunday
+        # is a working day in some geographies.
+        - time: '0 8 * * 6'
+    success:
+      mysql:
+    failure:
+      mysql:
+      smtp:
+        from: zuul@opendev.org
+        to: zuul-jobs-failures@lists.zuul-ci.org
+        subject: 'zuul-jobs @periodic-weekly failed'
+
 - pipeline:
     name: tag
     post-review: true