[FIX] l10n_it_edi_sdicoop: fix EDI notification logic

In some cases, Odoo's move state is unaligned to that on the
IAP Proxy Server, because the ACK message from Odoo to IAP
deletes all attachments from the EDI transactions on the IAP
without regard if they are with type "Send" or "Receive".

We fix both cases by making Odoo just look at the state and not
to the attachment when it's not needed, and it's only needed when
there is a rejection of the document being sent.

We reserve for the future a change to the ACK to only delete the
attachments by transmission type (Send/Receive) so that they don't
interfere.

Error case 1:
- Odoo client sends an invoice to the IAP Proxy
- The IAP proxy will send it to the SdI
- If everything goes well, the SdI will send a notification back
- The IAP proxy sees the notification and saves it
- The Odoo of the client downloads the notification and sends an ack
- The IAP proxy sees the ack and deletes the attachment
- (ERR!) The client resets to draft, modifies and re-confirms
- The state of his invoice is set again To Send
- Odoo tries to re-send the invoice with the same Id Transaction
- The notification for that Id Transaction is already on the IAP proxy
- Odoo client asks for changes, but just sees the old notification
- (-->) The old notif. has no attachment, so Odoo thinks there's no news
- The move in Odoo stays in the To Send state forever

Error case 2:
- Odoo client sends a Tax Integration for a Vendor Bill (reverse charge)
- The IAP proxy will send it to the SdI
- If everything goes well, the SdI will send the same Vendor Bill back
  as the client's CodiceDestinatario is actually the recipient in the XML
- The IAP proxy sees the file, the Id Transaction is the same
  for both the received and the sent documents
- The SdI sends a notification because the tax integration is OK
- The IAP proxy saves the notification, there are now two EDI
  transactions with the same Id Transaction.
- Odoo checks for new documents
- IAP proxy sends the document to Odoo
- Odoo sends an ACK for that
- (ERR!) the IAP proxy sees the ACK and clears the attachment
  from BOTH the records for sent and received document
- Odoo checks for documents updates and gets the record without
  the attachment
- (-->) The notification has no attachment, so Odoo thinks there's no news
- The move in Odoo stays in the To Send state forever

Ticket link: https://www.odoo.com/web#id=3194378&model=project.task


opw-3194378

closes odoo/odoo#113666

Signed-off-by: Josse Colpaert <jco@odoo.com>