PERF(repo): add PriorityClasses for workloads

- Create high-priority (1000) for critical infra
- Create medium-priority (500) for observability
- Create low-priority (100) as global default

priority-classes/manifests/kustomization.yaml

@@ -0,0 +1,5 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - priority-classes.yaml