Upload release images on tag

This uploads release images to dockerhub when we tag the repo.

Change-Id: Ic44a9d29a1e888d8d7874205b0025f286912b5e8

.zuul.yaml

@@ -39,6 +39,10 @@
         - context: .
           dockerfile: build/Dockerfile
           repository: zuul/zuul-operator
+          tags:
+            # If zuul.tag is defined: [ '3', '3.19', '3.19.0' ].  Only works for 3-component tags.
+            # Otherwise: ['latest']
+            "{{ zuul.tag is defined | ternary([zuul.get('tag', '').split('.')[0], '.'.join(zuul.get('tag', '').split('.')[:2]), zuul.get('tag', '')], ['latest']) }}"
 
 - secret:
     name: zuul-operator-dockerhub
@@ -100,3 +104,9 @@
     promote:
       jobs:
         - zuul-operator-promote-image
+    release:
+      jobs:
+        - zuul-operator-upload-image:
+            vars:
+              <<: *image_vars
+              upload_docker_image_promote: false