Update zoekt how to guide

What does this merge request do and why?

Advanced search does not need to be enabled locally to have Zoekt group search work.

How to set up and validate locally

1. Follow the instructions to enable Zoekt
2. Turn off Advanced search indexing and search in the Admin UI - Search Settings
3. Ensure that Exact code search is enabled in the user preferences (for whoever you logged in as)
4. Perform a group search for flightjs
5. Ensure that Exact code search (powered by Zoekt) is enabled. is shown in search results

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.