argocd: Deploy Argo CD

[Argo CD] is a Kubernetes-native GitOps/continuous deployment manager.
It monitors the state of Kubnernetes resources, such as Pods,
Deployments, ConfigMaps, Secrets, and Custom Resources, and synchronizes
them with their canonical definitions from a Git repository.

*Argo CD* consists of various components, including a Repository
Service, an Application Controller, a Notification Controller, and an
API server/Web UI.  It also has some optional components, such as a
bundled Dex server for authentication/authorization, and an
ApplicationSet controller, which we will not be using.

[Argo CD]: https://argo-cd.readthedocs.io/

argocd/hooks.yaml

@@ -0,0 +1,20 @@
+apiVersion: batch/v1
+kind: Job
+metadata:
+  generateName: jenkins-snapshot-
+  annotations:
+    argocd.argoproj.io/hook: PostSync
+spec:
+  template:
+    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