Build customers-api REST layer (Layer 3), mirroring catalog-api

8 routes over Customer + orders/payments sub-resources, proxying to
classic-models-api. openid-connect with RFC 8693 token exchange to
classic-models-api audience, rate-limiting, proxy-cache, audit-log —
same plugin set and structure as catalog-api's REST surface.

Not deployed: dev/gitrepository.yaml points at a gitea repo that
doesn't exist yet (kong-customers-api.git, 404). No MCP layer yet
either, unlike catalog-api.

kong/kustomization.yaml

@@ -0,0 +1,14 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - rest/service.yaml
+  - rest/routes.yaml
+  - rest/path-rewrite.yaml
+  - rest/path-rewrite-bindings.yaml
+  - rest/kongplugin.yaml
+  - rest/rate-limiting.yaml
+  - rest/proxy-cache.yaml
+  - rest/audit-log.yaml
+  - rest/audit-log-body-capture.yaml
+  - rest/audit-log-body-capture-bindings.yaml
+  - rest/pluginbindings.yaml