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

Makefile

@@ -11,6 +11,11 @@ kubeconform:
 	@ci/validate-apps.sh && \
 	ci/validate-clusters.sh
 
+# Generate JSON schemas from CRD definitions for kubeconform
+# Run when CRD versions change, then commit ci/crd-schemas/
+generate-schemas:
+	@ci/generate-crd-schemas.sh
+
 # Clean all generated manifests
 clean:
 	@rm -rf manifests/