Add the `res_users_settings_id` field on `res.users` so that it can be
used as a target for relateds that is not a x2many field.
closesodoo/odoo#90015
Related: odoo/upgrade#3479
Related: odoo/enterprise#26287
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>