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/applications/ntfy.yaml

@@ -0,0 +1,13 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: ntfy
+  namespace: argocd
+spec:
+  destination:
+    server: https://kubernetes.default.svc
+  project: default
+  source:
+    path: ntfy
+    repoURL: https://git.pyrocufflink.blue/infra/kubernetes.git
+    targetRevision: master