CLI: Validate JSON keymap input (#16261)

* Fix schema validator

It should use the passed schema.

* Add required attributes to keymap schema

* Rework subcommands to validate the JSON keymaps

The 'compile', 'flash' and 'json2c' subcommands were reworked to add
JSON keymap validation so error is reported for non-JSON and
non-compliant-JSON inputs.

* Fix required fields in keymap schema

* Add tests

* Fix compiling keymaps directly from keymap directory

* Schema should not require version for now.

data/schemas/keymap.jsonschema

@@ -53,5 +53,10 @@
             "type": "string",
             "description": "asdf"
         }
-    }
+    },
+    "required": [
+        "keyboard",
+        "layout",
+        "layers"
+    ]
 }