[FIX] hr, hr_contract: set contract end date when we archive the employee

1) If the contract is running when the employee is archived, we move the contract in the
   expired stage and we set the date of the archive wizard to the
   contract's end date.

2) If the contract has expired when the employee is archived, do not change the date.

task-3373275

closes odoo/odoo#126627

Signed-off-by: Sofie Gvaladze (sgv) <sgv@odoo.com>