feat: Add hardware metadata schema.

* Initial hardware metadata JSON schema.
* GH Action to validate all schemas for boards/shields.

app/scripts/west_commands/metadata.py

@@ -0,0 +1,59 @@
+# Copyright (c) 2021 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+'''Metadata command for ZMK.'''
+
+from functools import cached_property
+import glob
+import json
+from jsonschema import validate, ValidationError
+import os
+import sys
+import yaml
+from textwrap import dedent            # just for nicer code indentation
+
+from west.commands import WestCommand
+from west import log                   # use this for user output
+
+
+class Metadata(WestCommand):
+    def __init__(self):
+        super().__init__(
+            'metadata',  # gets stored as self.name
+            'ZMK hardware metadata commands',  # self.help
+            # self.description:
+            dedent('''Operate on the board/shield metadata.'''))
+
+    def do_add_parser(self, parser_adder):
+        parser = parser_adder.add_parser(self.name,
+                                         help=self.help,
+                                         description=self.description)
+
+        parser.add_argument('subcommand', default="check",
+                            help='The subcommand to run. Defaults to "check".', nargs="?")
+        return parser           # gets stored as self.parser
+
+    @cached_property
+    def schema(self):
+        return json.load(
+            open("../schema/hardware-metadata.schema.json", 'r'))
+
+    def validate_file(self, file):
+        print("Validating: " + file)
+        with open(file, 'r') as stream:
+            try:
+                validate(yaml.safe_load(stream), self.schema)
+            except yaml.YAMLError as exc:
+                print("Failed loading metadata yaml: " + file)
+                print(exc)
+                return False
+            except ValidationError as vexc:
+                print("Failed validation of: " + file)
+                print(vexc)
+                return False
+        return True
+
+    def do_run(self, args, unknown_args):
+        status = all([self.validate_file(f) for f in glob.glob(
+            "boards/**/*.zmk.yml", recursive=True)])
+
+        sys.exit(0 if status else 1)