feat(grafana): provision a Gotify contact point

Grafana gains one contact point, `gotify`, of type webhook. It posts to the
bridge in the notifications namespace because Gotify rejects a Grafana payload
with 400 "Field 'message' is required".

maxAlerts 0 keeps every alert in one request, and the bridge names the extra
count in the message body instead of dropping alerts.

k8s/infra/logging/grafana-values.yaml

@@ -209,3 +209,25 @@ sidecar:
       disableDelete: false
       foldersFromFilesStructure: true
     searchNamespace: ALL
+
+# ── Alerting ──────────────────────────────────────────────────────────────────
+# One contact point: Gotify. Gotify refuses Grafana's payload shape with
+# 400 "Field 'message' is required", so a bridge service translates the JSON
+# first (k8s/apps/gotify/bridge). Grafana posts to the bridge, the bridge posts
+# to /message with an app token.
+alerting:
+  contactpoints.yaml:
+    apiVersion: 1
+    contactPoints:
+      - orgId: 1
+        name: gotify
+        receivers:
+          - uid: gotify-webhook
+            type: webhook
+            disableResolveMessage: false
+            settings:
+              url: http://grafana-gotify-bridge.notifications.svc.cluster.local:8080/alert
+              httpMethod: POST
+              # 0 sends every alert in one request. The bridge names the extra
+              # count in the message body.
+              maxAlerts: 0