text: Title: exclude db from .gitignore
  Body: Hello
  
  Please, exclude db from .gitignore because it doesnt work with ci. Image can't start
  
  ```
  Traceback (most recent call last):
    File "/app/./venv/bin/libretranslate", line 8, in <module>
  Loaded support for 3 languages (4 models total)!
      sys.exit(main())
    File "/app/venv/lib/python3.10/site-packages/libretranslate/main.py", line 189, in main
      app = create_app(args)
    File "/app/venv/lib/python3.10/site-packages/libretranslate/app.py", line 220, in create_app
      os.mkdir(default_mp_dir)
  FileNotFoundError: [Errno 2] No such file or directory: '/app/db/prometheus'
  ```