Redirect root path requests to the tenants administration

When the `multitenancy_management_mode` is enabled.

In order to avoid infinite redirects when regular users try to access
the admin section, we're redirecting to the account page in this case.
Otherwise, the admin section would redirect to the root path, which
would redirect to the admin section, which would redirect to the root
path, and so on.

app/controllers/concerns/access_denied_handler.rb

@@ -4,7 +4,13 @@ module AccessDeniedHandler
   included do
     rescue_from CanCan::AccessDenied do |exception|
       respond_to do |format|
-        format.html { redirect_to main_app.root_path, alert: exception.message }
+        format.html do
+          if Rails.application.multitenancy_management_mode?
+            redirect_to main_app.account_path, alert: exception.message
+          else
+            redirect_to main_app.root_path, alert: exception.message
+          end
+        end
         format.json { render json: { error: exception.message }, status: :forbidden }
       end
     end