Push multiple Docker tags for image in CD.

This will allow Kubernetes resources that only pull images occasionally
(i.e., k8s jobs) to point to a static tag name, "latest", that is updated
regularly. It also means we can refer to that image in the k8s config
tracked in the repo, instead of out-of-date images.

deploy/azure/azure.yml

@@ -28,7 +28,7 @@ spec:
         fsGroup: 101
       containers:
         - name: atst
-          image: pwatat.azurecr.io/atat:4d14326ba77f1b3287b3c436a2d9be064bf4fba3
+          image: pwatat.azurecr.io/atat:latest
           resources:
             requests:
                memory: "500Mi"
@@ -140,7 +140,7 @@ spec:
         fsGroup: 101
       containers:
         - name: atst-worker
-          image: pwatat.azurecr.io/atat:4d14326ba77f1b3287b3c436a2d9be064bf4fba3
+          image: pwatat.azurecr.io/atat:latest
           args: [
             "/opt/atat/atst/.venv/bin/python",
             "/opt/atat/atst/.venv/bin/celery",