app menu: MR assigend without review added

What does this MR do and why?

Adds number of Assigned MRs that are not in code review into the main menu. Total merge requests does not include count of requests that are sent to code review.

Screenshots or screen recordings

How to set up and validate locally

1. create merge request and set yourself as Assignee (expected behaviour: badge should display 1)
2. set someone else as Reviewer (expected behaviour: badge should display 0)

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.