✨ feat: add development environment configuration and update sample data generation

[iShelar]

• Introduced a new development.env file for environment variable configuration.
• Updated README to reflect new task command for generating sample data.
• Added django:generate-sample-data task to Taskfile for easier sample data generation.
• Refactored factories in factories.py to use Wagtail factories and improved sample data generation logic in the management command.