Add JSON schema generation for kubeconform CRD validation

- ci/generate-schemas.sh extracts schemas from live cluster CRDs via kubectl
- Generated schemas committed to schemas/ for CI use
- Run `make schemas` to regenerate after CRD or K8s version changes
- validate-apps.sh and validate-clusters.sh check local schemas first
- CRD instances (Gateway, TLSRoute, Pooler, etc.) now validated instead of skipped
- CustomResourceDefinition meta-type still skipped (no schema exists upstream)

schemas/postgresql.cnpg.io/imagecatalog_v1.json

@@ -0,0 +1,54 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "apiVersion": {
+      "type": "string"
+    },
+    "kind": {
+      "type": "string"
+    },
+    "metadata": {
+      "type": "object"
+    },
+    "spec": {
+      "properties": {
+        "images": {
+          "items": {
+            "properties": {
+              "image": {
+                "type": "string"
+              },
+              "major": {
+                "minimum": 10,
+                "type": "integer"
+              }
+            },
+            "required": [
+              "image",
+              "major"
+            ],
+            "type": "object"
+          },
+          "maxItems": 8,
+          "minItems": 1,
+          "type": "array",
+          "x-kubernetes-validations": [
+            {
+              "message": "Images must have unique major versions",
+              "rule": "self.all(e, self.filter(f, f.major==e.major).size() == 1)"
+            }
+          ]
+        }
+      },
+      "required": [
+        "images"
+      ],
+      "type": "object"
+    }
+  },
+  "required": [
+    "metadata",
+    "spec"
+  ],
+  "type": "object"
+}