It's currently not possible to know which `pos.order` is linked to a
`sale.report`
Solution:
Add a field `order_reference` on model `sale.report`. This field refers
to either a "sale.order" or a "pos.order" record.
The field `order_reference` is used to count the number of distinct
orders. We cannot simply use count_distinct on the `order_id` because
there can be multiple sale.report with the same `order_id` but related
to different models (sale or POS order).
Part-of: odoo/odoo#116830
MerlinGuillaume
7bbec42f07