🗃️ Create and use a db dedicated user for backend

* Rename the db name (idfm_matrix_bot -> cer_db).
 * Remove unused bot database.
 * Create a dedicated user (cer_user/cer_password).

backend/main.py

@@ -24,7 +24,7 @@ API_KEY = environ.get("API_KEY")
 # TODO: Add error message if no key is given.
 
 # TODO: Remove postgresql+asyncpg from environ variable
-DB_PATH = "postgresql+asyncpg://postgres:postgres@127.0.0.1:5438/idfm"
+DB_PATH = "postgresql+asyncpg://cer_user:cer_password@127.0.0.1:5438/cer_db"
 
 
 app = FastAPI()