Docs: add FileTree Astro component and use it in pages

[julien-deramond]

Warning

This PR is in an early draft stage and currently supports dark mode only.

This pull request introduces a new custom Astro component to enhance the rendering of file trees within the documentation. It is based on a modified version of the Starlight FileTree Astro component, along with its related files.

Please note that the README.md file has been intentionally left unchanged. Since it is not rendered in the documentation, it still uses the original Markdown syntax.

Before:

Now:

Pages

• https://deploy-preview-41493--twbs-bootstrap.netlify.app/docs/5.3/customize/sass/
• https://deploy-preview-41493--twbs-bootstrap.netlify.app/docs/5.3/getting-started/contents/
• https://deploy-preview-41493--twbs-bootstrap.netlify.app/docs/5.3/getting-started/parcel/
• https://deploy-preview-41493--twbs-bootstrap.netlify.app/docs/5.3/getting-started/vite/
• https://deploy-preview-41493--twbs-bootstrap.netlify.app/docs/5.3/getting-started/webpack/

Remaining Tasks

• Add full support for both light and dark modes
• Replace Starlight-specific styles with Bootstrap variables and color tokens
• Refactor CSS rules to align with Bootstrap’s documentation style conventions
• Include proper attribution for reused Starlight code:
  • Add references and headers in relevant files
  • Link to the original sources and include licensing information