jenkins: Add Argo CD pre-sync hook

Argo CD will delete and re-create this Job each time it synchronizes the
*jenkins* application.  The job creates a snapshot of the Jenkins volume
using an HTTP request to the Longhorn UI.

jenkins/argocd-sync-hook.yaml

@@ -0,0 +1,25 @@
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: jenkins-snapshot-hook
+  namespace: jenkins
+  annotations:
+    argocd.argoproj.io/hook: PreSync
+    argocd.argoproj.io/hook-delete-policy: BeforeHookCreation
+spec:
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: jenkins-snapshot-hook
+    spec:
+      containers:
+      - name: jenkins-snapshot
+        image: docker.io/curlimages/curl
+        command:
+        - curl
+        - http://longhorn-frontend.longhorn-system/v1/volumes/pvc-4d42f4d3-2f9d-4edd-b82c-b51a385a3276?action=snapshotCreate
+        - -H
+        - 'Content-Type: application/json'
+        - -d
+        - '{}'
+      restartPolicy: Never

jenkins/kustomization.yaml

@@ -7,6 +7,7 @@ labels:
 
 resources:
 - jenkins.yaml
+- argocd-sync-hook.yaml
 
 configMapGenerator:
 - name: ssh-known-hosts