Add user event tracking to "your work" sidebar MR flyout menu

What does this MR do and why?

The merge requests submenu options in the "your work" sidebar lack snowplow event properties so user activity is not currently being tracked. This branch corrects the issue.

Screenshots or screen recordings

How to set up and validate locally

1. Enable snowplow-micro in your local GDK and open up the snowplow debugger
2. Visit a page in your GDK where the "your work" sidebar is visible
3. Click on one of the merge request submenu options in the fly-out menu
4. Observe that the event labels merge_requests_assigned and merge_requests_to_review are present in structured snowplow events upon clicking the "Assigned" and "Review requests" menu options respectively.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #389859 (closed)