Resolve "Add point of interest discussions to designs"

What does this MR do?

CE counterpart: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31276

Creates a possibility to add annotations to designs

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

Security

Closes #9489 (closed)

Closes #12731 (closed) (thanks to @xanf contribution)