Frontend: Add fork filter for Zoekt code search

Problem to solve

#411833 (closed) will introduce backend for filtering Zoekt by forks but this filter does not currently exist in the UI

Proposal

Exclude forks by default in Zoekt code search

Add a filter option (similar to how archived works) that will filter out forked projects.

The filter should only be applied to Zoekt code search tab for group scoped search only.

Global search is not currently supported for Zoekt.

Project scoped search should always search the project the user has selected so the filter does not need to be shown