Fix design management router

What does this MR do?

Changes the design management Vue Router to use history mode. This produces nicer URL's and also allows for issue note linking to working correctly.

CE backport https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31090

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64667

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Performance 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