[FIX] mail: groupby was using a wrong create_id field
[FIX] mail: groupby was using a wrong create_id field

Grouping mail activities by "Created by" was grouping on the
"create_uid" field which is always the admin user. New groupby
groups using the "create_user_id" field which is the real id
of the creator.

opw-1886369

closes odoo/odoo#27718
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo