Scrape k8up operator metrics (#512)

The k8up operator already serves Prometheus metrics (backup/check/prune job counts, controller-runtime) on its k8up-metrics Service, but nothing scrapes them, so backup health is invisible in VictoriaMetrics.

- add a VMServiceScrape for the k8up-metrics Service (port http, /metrics)

Reviewed-on: #512
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/k8up-system/kustomization.yaml

@@ -4,3 +4,4 @@ kind: Kustomization
 
 resources:
   - namespace.yaml
+  - vmservicescrape.yaml

apps/base/k8up-system/vmservicescrape.yaml

@@ -0,0 +1,15 @@
+---
+# Scrape the k8up operator metrics (k8up-metrics Service, port http :8080).
+apiVersion: operator.victoriametrics.com/v1beta1
+kind: VMServiceScrape
+metadata:
+  name: k8up
+  namespace: k8up-system
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: k8up
+      app.kubernetes.io/instance: k8up
+  endpoints:
+    - port: http
+      path: /metrics