Use VAT to identify existing `res.partner` instead of `email`

Cooperator assigns the subcription request "increment share" if found a soci validated with the same email.

There are cases where there are different users but with the same email.

1. SR con email@email
2. Validar SR crea nuevo res.partner con email email@email
3. Nueva SR (via form) con email@email
4. La SR se crea asociando ya el contacto creado al punto 2