[FIX] 11.0 partner_second_last_name required only if type = contact
[FIX] 11.0 partner_second_last_name required only if type = contact

Description of the issue/feature this PR addresses:

firstname, lastname and lastname2 fields should only be required if
contact `type` is `contact`. In partner_firstname module this is done
right with `('type', '=', 'contact')` leave in attrs required domain.
But in partner_second_last_name there is no such leave, so if the
contact is an address, the fields are mandatory too.

Current behavior:

Either firstname, lastname or lastname2 are mandatory when a contact is
not a company.

Desired behavior after PR is merged:

firstname, lastname or lastname2 are mandatory when the contact is of
type `contact`

microcom/partner-contact,brain-tec/partner-contact,microcom/partner-contact,brain-tec/partner-contact