feat(docs): Add aggregated metadata to website

Added /hardware-metadata.json to the ZMK website.
This gives external tools a way to grab all hardware metadata at once.

docs/src/hardware-metadata-static-plugin/index.js

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+//@ts-check
+"use strict";
+
+/** @typedef {import('../hardware-metadata').HardwareMetadata} HardwareMetadata */
+/** @typedef {HardwareMetadata & { directory: string}} LocatedHardwareMetadata */
+
+const fs = require("fs").promises;
+const glob = require("util").promisify(require("glob"));
+const path = require("path");
+const yaml = require("js-yaml");
+
+const BASE_DIR = "..";
+const METADATA_GLOB = path.posix.join(BASE_DIR, "app/boards/**/*.zmk.yml");
+
+/**
+ * @param {string} file
+ */
+async function readMetadata(file) {
+  /** @type HardwareMetadata[] */
+  // @ts-ignore
+  const documents = yaml.loadAll(await fs.readFile(file, "utf-8"));
+
+  return documents.map(
+    (metadata) =>
+      /** @type LocatedHardwareMetadata */
+      ({
+        ...metadata,
+        // External tools need a way to locate this hardware within the repo.
+        // Append each item's relative path.
+        directory: path.posix.dirname(path.posix.relative(BASE_DIR, file)),
+      })
+  );
+}
+
+async function aggregateMetadata() {
+  const files = await glob(METADATA_GLOB);
+  const data = await Promise.all(files.map(readMetadata));
+
+  return data.flat();
+}
+
+/**
+ * Aggregates .zmk.yml files and writes hardware-metadata.json to the site's
+ * static files post-build.
+ *
+ * This is very similar to hardware-metadata-collection-plugin but adjusts the
+ * output for consumption by external tools rather than the website build system.
+ *
+ * @type {import('@docusaurus/types').PluginModule}
+ */
+module.exports = function () {
+  return {
+    name: "hardware-metadata-static-plugin",
+
+    async postBuild({ outDir }) {
+      const hardware = await aggregateMetadata();
+
+      const hardwarePath = path.join(outDir, "hardware-metadata.json");
+      await fs.writeFile(hardwarePath, JSON.stringify(hardware));
+    },
+  };
+};