add subcatalog

xpublish_sample_stac/catalog/GDP_catalog/catalog.json

+{
+  "type": "Catalog",
+  "id": "nhgf-stac-catalog",
+  "stac_version": "1.0.0",
+  "description": "Sample NHGF STAC catalog.",
+  "links": [
+    {
+      "rel": "root",
+      "href": "../catalog.json",
+      "type": "application/json"
+    },    {
+      "rel": "parent",
+      "href": "../catalog.json",
+      "type": "application/json"
+    },
+    {
+      "rel": "item",
+      "href": "./GMO/item.json",
+      "type": "application/json"
+    },
+    {
+      "rel": "item",
+      "href": "./GMO_New/item.json",
+      "type": "application/json"
+    },
+    {
+      "rel": "item",
+      "href": "./PRISM/item.json",
+      "type": "application/json"
+    },
+    {
+      "rel": "item",
+      "href": "./PRISM_v2/item.json",
+      "type": "application/json"
+    },
+    {
+      "rel": "item",
+      "href": "./UoIMETDATA/item.json",
+      "type": "application/json"
+    }
+  ],
+  "stac_extensions": []
+}

xpublish_sample_stac/catalog/catalog.json

@@ -16,27 +16,7 @@
     },
     {
       "rel": "child",
-      "href": "./GMO/item.json",
-      "type": "application/json"
-    },
-    {
-      "rel": "child",
-      "href": "./GMO_New/item.json",
-      "type": "application/json"
-    },
-    {
-      "rel": "child",
-      "href": "./PRISM/item.json",
-      "type": "application/json"
-    },
-    {
-      "rel": "child",
-      "href": "./PRISM_v2/item.json",
-      "type": "application/json"
-    },
-    {
-      "rel": "child",
-      "href": "./UoIMETDATA/item.json",
+      "href": "./GDP_catalog/catalog.json",
       "type": "application/json"
     }
   ],