Frontend: Add fork filter for Zoekt code search

What does this MR do and why?

Added include forks filter for zoekt search results.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Make sure advanced search is installed and enabled
2. Make sure you enable zoekt.
3. In rails console enable the experiment fully

   echo "Feature.enable(:search_add_fork_filter_to_zoekt)" | gdk rails c

4. Visit any group or project member pages such as http://127.0.0.1:3000/groups/flightjs/-/group_members
5. Click the invite members button.

Related to #442654