adds field_name data on category and filter lists in the search panel template so it can be used to identify their field. this improvement is used in the drag & drop features introduced in the documents search panel (https://github.com/odoo/enterprise/pull/4805). Task: #1998014 closes odoo/odoo#34813 Signed-off-by: Martin Geubelle (mge) <mge@openerp.com>