Add Project.cached_count method (CE up-port)

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

app/models/project.rb

@@ -408,6 +408,12 @@ class Project < ActiveRecord::Base
 
       joins(join_body).reorder('join_note_counts.amount DESC')
     end
+
+    def cached_count
+      Rails.cache.fetch('total_project_count', expires_in: 5.minutes) do
+        Project.count
+      end
+    end
   end
 
   def repository_storage_path