Update nav_item_link selector to nav-item-link

What does this MR do and why?

Update nav_item_link data-qa-selector to nav-item-link data-testid across multiple pages.

This is joint effort based on gitlab-org/quality/quality-engineering/team-tasks#1735

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.