chore: use selfhosted-meilisearch as docs search engine (#357)

使用自建的 Meilisearch 作为文档搜索引擎，代替 Algolia。

/kind improvement

```release-note
None
```

src/theme/SearchBar.js

@@ -0,0 +1,25 @@
+import React, { useEffect } from "react";
+import "meilisearch-docsearch/css";
+
+export default function SearchBarWrapper(props) {
+  useEffect(() => {
+    const docsearch = require("meilisearch-docsearch").default;
+
+    const destroy = docsearch({
+      container: "#docsearch",
+      host: "https://docsearch.halo.run",
+      // Default Search API Key
+      // Use it to search from the frontend
+      apiKey:
+        "4b16205faa360eaa1ee5add67c0d265a4ca1e898ffbea199fe23d487a24c9bc8",
+      indexUid: "docs",
+    });
+
+    return () => destroy();
+  }, []);
+  return (
+    <>
+      <div id="docsearch"></div>
+    </>
+  );
+}