feat(ci): add CRD schema generation for kubeconform validation

Add scripts to extract OpenAPI v3 schemas from CRD definitions in all
kustomize overlays and write JSON schema files to ci/crd-schemas/ for
kubeconform validation. This allows kubeconform to validate CRD instances
(Elasticsearch, Kibana, CNPG Cluster, VictoriaMetrics, etc.) instead of
skipping or erroring on them.

- ci/generate-crd-schemas.py: extracts schemas from CRD YAML on stdin
- ci/generate-crd-schemas.sh: iterates overlays, pipes to Python script
- ci/validate-apps.sh, ci/validate-clusters.sh: add local schema-location fallback
- Makefile: add generate-schemas target
- add generate-schemas step to kubeconform woodpecker pipeline so schemas

.woodpecker/kubeconform.yaml

@@ -2,6 +2,21 @@ when:
   - event: pull_request
 
 steps:
+  - name: generate-schemas
+    image: git.unkin.net/unkin/almalinux9-kubetest:20260319
+    commands:
+      - make generate-schemas
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 512Mi
+            cpu: 1
+          limits:
+            memory: 2Gi
+            cpu: 2
+
   - name: kubeconform
     image: git.unkin.net/unkin/almalinux9-kubetest:20260319
     commands: