Add JSON schema generation for kubeconform CRD validation

- ci/generate-schemas.sh fetches CRDs from the cluster via kubectl, supplements
  with offline CRD manifests (ArgoCD, Gateway API) and Kubernetes swagger spec
- Schemas use Datree catalog convention: <group>/<Kind>_<version>.json
- validate-apps.sh and validate-clusters.sh check local schemas first
- Makefile schemas target runs before kubeconform

.gitignore

@@ -1,2 +1,3 @@
 manifests/
+schemas/
 apps/**/charts/