[IMP] partner_company_group: Add one2many counterpart for company_group_id

TT34815

partner_company_group/models/res_partner.py

@@ -10,6 +10,11 @@ class Contact(models.Model):
     company_group_id = fields.Many2one(
         "res.partner", "Company group", domain=[("is_company", "=", True)]
     )
+    company_group_member_ids = fields.One2many(
+        comodel_name="res.partner",
+        inverse_name="company_group_id",
+        string="Company group members",
+    )
 
     def _commercial_fields(self):
         return super()._commercial_fields() + ["company_group_id"]