[ADD] l10n_it_edi: Electronic invoicing Italy

- Generate e-invoice in xml when validating invoice
- e-invoice is sent via PEC mail and attached to the invoice
- electronic vendor bills and error/receipt messages can
be received through an IMAP incoming pec server
(configured in settings > technical)

We use the pec mail system to send invoices.  We don't manage
signed invoices for B2G.

Configuration is done on the company and the receiving partners
should have the correct codice fiscale / TVA.  On the taxes,
you might need to configure the exonerations.

You will need to configure the government mail address on the
company.  (sdi01...)  You might need to modify after the first
incoming message.

closes odoo/odoo#30845