Design system documentation

[bmlancien]

Summary of the discussion

• Create a first draft in the OEP design system documentation

Type of change (CHANGELOG.md)

Documentation updates

• Added documentation for Design System and Accessibility (#1716)

Workflow checklist

Automation

Closes #1709

PR-Assignee

• [ ] 🐙 Follow the workflow in CONTRIBUTING.md
• [ ] 📝 Update the CHANGELOG.md
• [ ] 📙 Update the documentation on mkdocs

Reviewer

• [ ] 🐙 Follow the Reviewer Guidelines
• [ ] 🐙 Provided feedback and show sufficient appreciation for the work done