Add default_branch Filter for use on struct templates

[httpdss]

Overview

This PR introduces a new default_branch filter, enabling users to dynamically fetch the default branch name of a specified GitHub repository. This feature enhances the automation and accuracy of project templates.

Changes

• Documentation:
  • Updated README.md and README.es.md with detailed examples of how to use the default_branch filter.
• Filter Implementation:
  • Added get_default_branch function in filters.py to fetch the default branch using the GitHub API.
  • Integrated the default_branch filter into the Jinja2 environment in template_renderer.py.
• Code Adjustments:
  • Updated template_renderer.py to support the new filter.

Justification

The default_branch filter allows users to seamlessly incorporate the default branch name of a GitHub repository into their templates, ensuring consistency and reducing manual input. This feature is particularly useful in CI/CD pipelines and dynamic project configurations.

Impact

• Improved flexibility and automation in project templates.
• Requires a valid GitHub token for private repository access, ensuring secure API interactions.
• Maintains backward compatibility with existing templates.