Frontend work for regex filter on Zoekt code search

What does this MR do and why?

Added regular expression button.

MR acceptance checklist

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable regular expression feature flag

   echo 'Feature.enable(:zoekt_exact_search)' | rails c

2. Make sure advanced search is installed and enabled
3. Make sure you enable zoekt.
4. Visit http://gdk.test:3000/search?search=test*&project_id=PROJECT_WITH_ZOEKT_ENABLED&group_id=GROUP_WITH_ZOEKT_ENABLED&search_code=true&scope=blobs
5. Test search with regular expression toggle enabled/disabled

Related to #435777 (closed)