Add system-config and zuul to OpenDev tenant for jobs

This adds repos to the OpenDev tenant so that jobs defined in their
repos may be used in that tenant.  Specifically, we're looking to
run third-party-check builds of Gerrit and Zuul on changes to
upstream Gerrit repos.  The actual jobs we run there are likely to
be defined in the system-config and zuul repos.

Change-Id: I41b345246f2012d15d969524b5879c9da32b708d

zuul/main.yaml

@@ -17,6 +17,13 @@
           - vexxhost/ansible-role-wireguard
           - vexxhost/kue
           - vexxhost/openstack-monitoring
+          # Include some projects with job config for cross-tenant
+          # jobs
+          - include: [job, secret, nodeset]
+            projects:
+              - opendev/system-config  # TODO: move to this tenant for
+                                       # real
+              - zuul/zuul
           # Include some projects without config for use in
           # required-projects
           - openstack/magnum: