Resolve "Update Design Management documentation"

What does this MR do?

This MR is a part of the work for moving Design Management app to the Issue description. In this part, we update the documentation related to Design Management with new screenshots/description where necessary, and we enable the design_management_moved feature flag by default.

Change	MR
Create a new Design Management app to be displayed behind the feature flag	!34932 (merged)
Refactor Design Management app to be displayed on the Issue instead of tabs	!35042 (merged)
Refactor Design management application to match new visual styles	!35746 (merged)
Update Design Management documentation	👉🏻 You are here
Make a cleanup after Design Management feature flag is removed	TBD

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines

Closes #223196 (closed)