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
- ci/crd-schemas/: 67 generated schemas (cert-manager, cnpg, elastic, victoriametrics, argocd, gateway)
- .pre-commit-config.yaml: raise large-file limit to 2 MB for generated schemas

Run `make generate-schemas` to regenerate after CRD version changes.

ci/crd-schemas/postgresql.cnpg.io/failoverquorum_v1.json

@@ -0,0 +1,46 @@
+{
+  "$schema": "http://json-schema.org/schema#",
+  "description": "FailoverQuorum contains the information about the current failover\nquorum status of a PG cluster. It is updated by the instance manager\nof the primary node and reset to zero by the operator to trigger\nan update.",
+  "properties": {
+    "apiVersion": {
+      "description": "APIVersion defines the versioned schema of this representation of an object.\nServers should convert recognized schemas to the latest internal value, and\nmay reject unrecognized values.\nMore info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources",
+      "type": "string"
+    },
+    "kind": {
+      "description": "Kind is a string value representing the REST resource this object represents.\nServers may infer this from the endpoint the client submits requests to.\nCannot be updated.\nIn CamelCase.\nMore info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds",
+      "type": "string"
+    },
+    "metadata": {
+      "type": "object"
+    },
+    "status": {
+      "description": "Most recently observed status of the failover quorum.",
+      "properties": {
+        "method": {
+          "description": "Contains the latest reported Method value.",
+          "type": "string"
+        },
+        "primary": {
+          "description": "Primary is the name of the primary instance that updated\nthis object the latest time.",
+          "type": "string"
+        },
+        "standbyNames": {
+          "description": "StandbyNames is the list of potentially synchronous\ninstance names.",
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
+        "standbyNumber": {
+          "description": "StandbyNumber is the number of synchronous standbys that transactions\nneed to wait for replies from.",
+          "type": "integer"
+        }
+      },
+      "type": "object"
+    }
+  },
+  "required": [
+    "metadata"
+  ],
+  "type": "object"
+}