Add get_user method

services/repository.py

@@ -13,3 +13,8 @@ class Repo:
             "VALUES ($1, $2) ON CONFLICT (user_id) DO NOTHING",
             user_id, chat_id
         )
+
+    async def get_user(self, user_id: int):
+        return await self.conn.fetchval(
+            "SELECT user_id FROM users WHERE user_id = $1", user_id
+        )