Add Minimal Mode option to cookiecutter template

[josephwilson8-nhs]

Description:
Add a minimal mode option in the cookiecutter prompts that strips the template back to essentials:

• Package files (pyproject.toml, etc.)
• Source code folder
• Tests folder
• Data folder

Acceptance Criteria:

• Add 'minimal_mode' prompt to cookiecutter.json
• Conditional logic in templates to exclude non-essential files when minimal mode is selected
• Documentation updated to explain minimal mode option

Priority: Medium
Type: Feature