Disable Turbo's prefetch, which became default in turbo-rails 2.x

Fixes #3701

Author: mshibuya

app/views/layouts/rails_admin/_head.html.erb

@@ -2,6 +2,7 @@
 <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
 <meta content="width=device-width, initial-scale=1" name="viewport; charset=utf-8">
 <meta content="NONE,NOARCHIVE" name="robots">
+<meta content="false" name="turbo-prefetch">
 <%= csrf_meta_tag %>
 <% case RailsAdmin::config.asset_source
    when :webpacker %>

spec/integration/rails_admin_spec.rb

@@ -204,6 +204,13 @@
       is_expected.to have_content 'Player failed to be updated'
       is_expected.to have_css '.filtering-select[data-input-for="player_team_id"]'
     end
+
+    it 'does not prefetch pages' do
+      allow_any_instance_of(RailsAdmin::Config::Actions::Index).to receive(:controller).and_raise('index prefetched')
+      visit dashboard_path
+      find('.sidebar a.nav-link[href$="/player"]').hover
+      sleep 0.3 # Turbo waits 100ms before prefetch
+    end
   end
 
   describe 'dom_ready events', js: true do