Add new environment variable for base URL and update code to use it

[Stevo-G-Swag]

• main.py
  • Add initialization for the base URL from environment variables
  • Raise ValueError if BASE_URL is not found in environment variables
• .env.example
  • Add BASE_URL environment variable
• settings.py
  • Create a settings page to manage and edit environment variables dynamically
• tests/
  • Add test functions to verify settings page and update settings functionality
• pytest.ini
  • Add pytest configuration file to specify test discovery settings