Create a new Design Management app to be behind the feature flag

What does this MR do?

To make a refactoring process smoother and easier to roll out, we need to create a feature flag and create a 'copy' of Design Management application to be mounted when this feature flag is on. This is the first MR in a set of changes to migrate Design Management app to the Issue description

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

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #223192 (closed)