Improve accessibility and navigation (ie_fixes)

[IE-smhi]

Improve the accessibility, navigability and search functionality of the documentation.

This issue will address:

1. Implementation of the Doxygen Awesome CSS:
   • Add the Doxygen Awesome CSS for a cleaner and responsive design.
2. Upgrade Doxygen Version:
   • Ensure the project uses Doxygen version 1.9.1 for improved functionality .
3. Enhance Navigation:
   • Enable the navigation tree to provide a more intuitive user experience, making the documentation easier to browse.
4. Improve Search Functionality:
   • Ensure the search bar works effectively, making it easier for users to find content across all documentation pages.

Tasks:

• Integrate Doxygen Awesome CSS.
• Upgrade to Doxygen 1.9.1.
• Ensure the navigation tree works across all documentation pages.
• Ensure the search bar works properly and indexes the right content (HTML pages).