[FIX] mrp: search workorders by finished_lot_id

Before this commit, it was impossible to search workorders by their
finished_lot_id as there was no search function for this field.
This commit adds the search function.

opw-3330126
community PR: https://github.com/odoo/odoo/pull/123223



closes odoo/odoo#123223

Signed-off-by: William Henrotin (whe) <whe@odoo.com>