Add config.h and rules.mk support for data driven keymaps (#12859)

* Add config.h and rules.mk support for data driven keymaps

* tidy up after rebase

* Rename key as it can contain more than just keyboard overrides

* tidy up after rebase

* Add validation

data/schemas/keymap.jsonschema

@@ -0,0 +1,24 @@
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "$id": "qmk.keymap.v1",
+    "title": "Keymap Information",
+    "type": "object",
+    "properties": {
+        "author": {"$ref": "qmk.definitions.v1#/text_identifier"},
+        "keyboard": {"$ref": "qmk.definitions.v1#/text_identifier"},
+        "keymap": {"$ref": "qmk.definitions.v1#/text_identifier"},
+        "layout": {"$ref": "qmk.definitions.v1#/layout_macro"},
+        "layers": {
+            "type": "array",
+            "items": {
+                "type": "array",
+                "items": {"type": "string"}
+            }
+        },
+        "config": {"$ref": "qmk.keyboard.v1"},
+        "notes": {
+            "type": "string",
+            "description": "asdf"
+        }
+    }
+}