victoria-metrics: Send alerts via ntfy

I don't like having alerts sent by e-mail.  Since I don't get e-mail
notifications on my watch, I often do not see alerts for quite some
time.  They are also much harder to read in an e-mail client (Fastmail
web an K-9 Mail both display them poorly).  I would much rather have
them delivered via _ntfy_, just like all the rest of the ephemeral
notifications I receive.

Fortunately, it is easy enough to integrate Alertmanager and _ntfy_
using the webhook notifier in Alertmanager.  Since _ntfy_ does not
natively support the Alertmanager webhook API, though, a bridge is
necessary to translate from one data format to the other.  There are a
few options for this bridge, but I chose
[alexbakker/alertmanager-ntfy][0] because it looked the most complete
while also having the simplest configuration format.  Sadly, it does not
expose any Prometheus metrics itself, and since it's deployed in the
_victoria-metrics_ namespace, it needs to be explicitly excluded from
the VMAgent scrape configuration.

[0]: https://github.com/alexbakker/alertmanager-ntfy

victoria-metrics/alertmanager-ntfy.yaml

@@ -0,0 +1,69 @@
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: alertmanager-ntfy
+  labels:
+    app.kubernetes.io/name: alertmanager-ntfy
+    app.kubernetes.io/component: alertmanager-ntfy
+spec:
+  ports:
+  - port: 8000
+    name: alertmanager-ntfy
+  selector:
+    app.kubernetes.io/name: alertmanager-ntfy
+    app.kubernetes.io/component: alertmanager-ntfy
+
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: alertmanager-ntfy
+  labels:
+    app.kubernetes.io/name: alertmanager-ntfy
+    app.kubernetes.io/component: alertmanager-ntfy
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: alertmanager-ntfy
+      app.kubernetes.io/component: alertmanager-ntfy
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: alertmanager-ntfy
+        app.kubernetes.io/component: alertmanager-ntfy
+    spec:
+      containers:
+      - name: alertmanager-ntfy
+        image: git.pyrocufflink.net/containerimages/alertmanager-ntfy
+        args:
+        - --configs=/config/config.yml
+        ports:
+        - containerPort: 8000
+          name: http
+        readinessProbe: &probe
+          tcpSocket:
+            port: http
+          periodSeconds: 60
+        startupProbe:
+          <<: *probe
+          periodSeconds: 1
+          successThreshold: 1
+          failureThreshold: 30
+          timeoutSeconds: 1
+        securityContext:
+          runAsNonRoot: true
+          readOnlyRootFilesystem: true
+        volumeMounts:
+        - mountPath: /config
+          name: config
+          readOnly: true
+      securityContext:
+        fsGroup: 21447
+        runAsGroup: 21447
+        runAsNonRoot: true
+        runAsUser: 21447
+      volumes:
+      - name: config
+        configMap:
+          name: alertmanager-ntfy