Finish admin dashboard and update sql code

backend/utils/database.js

@@ -0,0 +1,12 @@
+const mysql = require("mysql2");
+
+//Create a pool of connections to allow multiple query happen at the same time
+const pool = mysql.createPool({
+  host: "localhost",
+  user: "root",
+  database: "Marketplace",
+  password: "12345678",
+});
+
+//Export a promise for promise-based query
+module.exports = pool.promise();