FEATURE: Allow admins to permanently delete posts and topics (#14406)

Sometimes administrators want to permanently delete posts and topics
from the database. To make sure that this is done for a good reasons,
administrators can do this only after one minute has passed since the
post was deleted or immediately if another administrator does it.

lib/guardian.rb

@@ -172,6 +172,10 @@ class Guardian
     can_do?(:delete, obj)
   end
 
+  def can_permanently_delete?(obj)
+    can_do?(:permanently_delete, obj)
+  end
+
   def can_moderate?(obj)
     obj && authenticated? && !is_silenced? && (
       is_staff? ||