[IMP]HR :Set a user as follower when Manager encode something in holida...

...y and expense .
https://www.odoo.com/web#id=10455&view_type=form&model=project.task&action=327
pad: https://pad.odoo.com/p/r.SeseD2mZFpiLBNT8
Shouldn't this field become a related then ? I don't know if having a user_id different from employee_id.user_id is requested by the model or if a related can be used.