fix: keep DB migration hook logs inspectable after deployment

Switch hook-delete-policy from hook-succeeded to before-hook-creation on
both the pre-upgrade and post-upgrade migration Jobs. hook-succeeded
deleted the Job immediately on success, making post-deploy log
inspection impossible. before-hook-creation keeps the most recent run's
Job and logs around (inspectable via kubectl logs job/<name>) and only
removes the previous Job when the next deployment fires the hook,
avoiding name conflicts and accumulation.

Part-of: <http://gitlab.vnc.biz/uxf/vnctalk-prosody/-/merge_requests/3>

helm/prosody/templates/db-migration-post-upgrade.yaml

@@ -8,7 +8,7 @@ metadata:
   annotations:
     helm.sh/hook: post-install,post-upgrade
     helm.sh/hook-weight: "5"
-    helm.sh/hook-delete-policy: hook-succeeded
+    helm.sh/hook-delete-policy: before-hook-creation
 spec:
   backoffLimit: 0
   template:

helm/prosody/templates/db-migration-pre-upgrade.yaml

@@ -8,7 +8,7 @@ metadata:
   annotations:
     helm.sh/hook: pre-upgrade
     helm.sh/hook-weight: "-5"
-    helm.sh/hook-delete-policy: hook-succeeded
+    helm.sh/hook-delete-policy: before-hook-creation
 spec:
   backoffLimit: 0
   template: