[IMP] *: use _read_group instead of read_group

This commit modifies most of the usages of read_group and uses
_read_group instead. _read_group doesn't join automatically on the
many2one fields when no order_by is specified, making it more performant
when the "name" of the many2one is not relevant, which is the case for
most back-end cases

closes odoo/odoo#84908

Task-id: 2479334
Related: odoo/enterprise#24877
Signed-off-by: Raphael Collet <rco@odoo.com>