Followup e26a1175d7c33746bddbc858ad89e68cc14beefe
Adds extra functionality and tests for the admin search modal.
* Show third level plugin config pages in search, e.g. AI Usage
* Remember last used search filters
* Allow navigating search results with keyboard, using tab or up/down
and enter to go to result
* Add a placeholder beneath search input to tell the admin what to do
* Add a full page search at `/admin/search` which can be reached from
pressing Enter on the search input
* Add specs for modal and full page search
* Change admin sidebar filter "no results found" to point to full page
search
* Add keyboard shortcut help to modal for admin search
