schema: metadata at the top level

Allows a new object under the top-level key `metadata` which contains a
`generators` property. This property is a list of all generators involved
in the creation of a manifest.

Each generator can add its name and version to this list.

Signed-off-by: Simon de Vlieger <supakeen@redhat.com>

schemas/osbuild2.json

@@ -19,6 +19,9 @@
       "enum": [
         "2"
       ]
+    },
+    "metadata": {
+      "$ref": "#/definitions/metadata"
     }
   },
   "definitions": {
@@ -83,6 +86,31 @@
         }
       }
     },
+    "metadata": {
+      "title": "Metadata information for a manifest",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "generators": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "additionalProperties": false,
+            "required": [
+              "name"
+            ],
+            "properties": {
+              "name": {
+                "type": "string"
+              },
+              "version": {
+                "type": "string"
+              }
+            }
+          }
+        }
+      }
+    },
     "mounts": {
       "title": "Collection of mount points for a stage",
       "type": "array",