Used cached value of project count to reduce DB load

Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG

@@ -90,6 +90,7 @@ v 8.11.0 (unreleased)
   - Sort folders with submodules in Files view !5521
 
 v 8.10.5 (unreleased)
+  - Cache project count for 5 minutes to reduce DB load
 
 v 8.10.4
   - Don't close referenced upstream issues from a forked project.

app/views/admin/dashboard/index.html.haml

@@ -112,7 +112,7 @@
           %h4 Projects
           .data
             = link_to admin_namespaces_projects_path do
-              %h1= number_with_delimiter(Project.count)
+              %h1= number_with_delimiter(Project.cached_count)
             %hr
             = link_to('New Project', new_project_path, class: "btn btn-new")
       .col-sm-4