Resolve "Re-arrange help-related user menu items into new Help menu"

What does this MR do?

• Moves "Help", "Contribute to Gitlab", and "Get a free instance health check" (EE only) to a specific Help menu dropdown icon

Help dropdown menu

Current user dropdown menu

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/50728

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #50728 (closed)