Add file matchers to image build jobs

This will allow us to make changes to provider configuration
without rebuilding images every time.

Add the noop job for the cases where no other job would run.

Change-Id: Id9de7758ddeb675fb298fbb0edf4fa398e8bec71

zuul.d/jobs.yaml

@@ -16,6 +16,10 @@
       - playbooks/opendev-build-diskimage-base/pre.yaml
     post-run:
       - playbooks/opendev-build-diskimage-base/post.yaml
+    files:
+      - 'dib-elements/.*'
+      - 'playbooks/opendev-build-diskimage-base/.*'
+      - 'roles/make-source-repositories-cache/.*'
     vars:
       # TODO(corvus): This will eventually be supplied by Zuul
       build_diskimage_formats:

zuul.d/project.yaml

@@ -1,9 +1,11 @@
 - project:
     check:
       jobs:
+        - noop
         - opendev-build-diskimage-debian-bullseye
     gate:
       jobs:
+        - noop
         - opendev-build-diskimage-debian-bullseye:
             secrets:
               - name: image_upload_secret