Invoices are sent after the transaction commits

Commit message

[IMP] account: send invoices in postcommit

When a payment transaction creates invoices and then sends them, by
email and through EDI to the government, a single concurrent update can
make the whole process fail at once. This mostly happens when the
customer pays through the portal, as the invoice is then created from
the payment.

Sending to the government is the dangerous part: invoice 01 can be sent
to the government (e.g. with l10n_in_edi) and then the whole transaction
gets rolled back, so the invoice does not even exist in Odoo anymore.
The numbering on the government side and in Odoo then no longer match.

To avoid that, the invoices are now only sent once the transaction that
created them is committed, in a new cursor. Since the invoices are
locked while being sent, the result of the sending is always recorded
in Odoo. The invoices that cannot be sent after the commit (locked by
another transaction, or failing) keep their `sending_data` and are
processed later by the sending cron.

A dedicated method is added in account and used in sale and
sale_loyalty instead of `_generate_and_send_invoices`, because the
latter returns the generated attachments, which the wizard uses to
inform the user directly, and a postponed call cannot return anything.

The sending cron now also uses the result of `try_lock_for_update`, so
that it only processes the invoices it could actually lock.

opw-5029676