Move search bar to top nav to test usage changes

What does this MR do and why?

This is usability experiment that will allow us to move search button to the top right corner for a group of users.

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

mobile

light	dark

How to set up and validate locally

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

1. In rails console enable the experiment fully

   Feature.enable(:search_button_top_right)

2. Visit any page http://127.0.0.1:3000
3. Test search button

Related to #480341 (closed)

spec/features/admin/admin_projects_spec.rb

@@ -7,6 +7,7 @@
   include Features::InviteMembersModalHelpers
   include Spec::Support::Helpers::ModalHelpers
   include ListboxHelpers
+  include MobileHelpers
 
   let_it_be_with_reload(:user) { create :user }
   let_it_be_with_reload(:project) { create(:project, :with_namespace_settings) }
@@ -175,8 +176,16 @@
     end
   end
 
-  describe 'project edit' do
-    it 'shows all breadcrumbs', :js do
+  describe 'project edit', :js do
+    before do
+      resize_window(1920, 1080)
+    end
+
+    after do
+      restore_window_size
+    end
+
+    it 'shows all breadcrumbs' do
       project_params = { id: project.to_param, namespace_id: project.namespace.to_param }
       visit edit_admin_namespace_project_path(project_params)