Super sidebar navigation read current page to screen-readers

What does this MR do and why?

Add aria-current to super sidebar navigation item <a> when isActive is true

Screenshots or screen recordings

Before	After
CleanShot_2023-03-09_at_15.49.01	CleanShot_2023-03-09_at_15.47.33

How to set up and validate locally

• Enable the feature flag in rails console with rails c

Feature.enable(:super_sidebar_nav)

• Enable the "New navigation" setting toggle from the user dropdown

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 #394971 (closed)