[WIP] feat: support design tokens and paragon 23

[dcoa]

This PR updates frontend app learning to support CSS variables and the corresponding paragon design tokens.

Changes implemented

• Replace Paragon SCSS variables with CSS variables.
• Replace deprecated components (Input, Modal, +/- font-awesome icons)

Important

This PR requires a compatible version with paragon 23 of dependencies because of that the following PRs need to be merged first:

• feat: adds support for loading external theme CSS for MFEs  frontend-platform#689
• [BD-46] feat: added support Paragon design tokens frontend-component-header#351
• [BD-46] feat: added support Paragon design tokens frontend-component-footer#303
• [WIP] chore: update paragon to a version to 23 frontend-lib-special-exams#159

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[bradenmacdonald]

Nice, thanks! Let me know when this is ready for review.