fix: On Supplier proposal external contact type is SERVICE not CUSTOMER

[FHenry]

On supplier proposal set external contact à "commercial". the name of this contact is not display in destinaries address box

[eldy]

Note: SERVICE is dedicated for the contact "performing the prestation".
The correct code value is "CUSTOMER" (if we want to match same other cases rules). But this entry was not created by default in v22, so i image a lot of users used the SERVICE entry as the contact following up the proposal.

The missing entry and code will be added in v24.