Add back periodic jobs

We would like to monitor the sf-operator CI job results in OpenSearch [1].
The CI results from the patch set unit are not equal with real results,
because some patch set can be broken from the beginning.
The periodic job will be triggered each 12 hours.

[1] https://opensearch.rdoproject.org

Depends-On: https://softwarefactory-project.io/r/c/sf-zuul-jobs-config/+/30499

Change-Id: I8ea601cfbbf7987b7121bb12ee0729860ab16c65

zuul.d/project.yaml

@@ -14,3 +14,8 @@
     release:
       jobs:
         - sf-operator-publish-olm-bundle-image
+    periodic-12h:
+      jobs:
+        - sf-operator-olm
+        - sf-operator-upgrade
+        - sf-operator-standalone