do not ever allow setting database_config_whitelist to database

Signed-off-by: nicole mikołajczyk <git@mkljczk.pl>

lib/pleroma/web/admin_api/controllers/config_controller.ex

@@ -174,6 +174,8 @@ defmodule Pleroma.Web.AdminAPI.ConfigController do
     end
   end
 
+  defp whitelisted_config?(:pleroma, :database_config_whitelist), do: false
+
   defp whitelisted_config?(group, key) do
     if whitelisted_configs = Config.get(:database_config_whitelist) do
       Enum.any?(whitelisted_configs, fn