Allow importing DuckDB databases

[tobilg]

It'd be great to be able to import (attach) DuckDB database files as well, similar to CSV, Parquet and Arrow files.

The code I'm currently using is basically this:

const loadDatabase = async (db: AsyncDuckDB, acceptedFile: File) => {
    try {
      const fileName = acceptedFile.name.replace(".duckdb", "");
      // Connect to the database
      const cid = await db.connectInternal();
      // Register the file
      await db.registerFileBuffer(fileName, new Uint8Array(await acceptedFile.arrayBuffer()));
      // Attach the database
      await db.runQuery(cid, `ATTACH '${fileName}' (READ_ONLY)`);
      // Disconnect from the database
      await db.disconnect(cid);
    } catch (err: any) {
      console.log(err);
    }
  }