[ADD] l10n_sa_edi: Implement Saudi ZATCA invoicing standards

The ZATCA edi has an onboarding process which happens per journal.
A private key is generated for the company and with the data from
the company and journal a CSR is made to get a certificate to sign the
invoices.  In that process that contains multiple steps (see account_journal.py),
we also have to send the compliance files which are some example (simplified or not)
invoices/debit and credit notes.  We have a separate folder with those files
and also use them in the tests.  For the onboarding, they still need to be signed however.

For the sending of the customer invoices themselves, UBL 2.1 is used, but
with ZATCA style adaptations.  That is why we inherit from that class
to be able to add those specific adaptations.  This UBL needs to be
signed XadeS and in this case we need to do the hash with the sign information
present but with empty tags.

For ZATCA invoices, as is the case with Ticketbai, the previous hash is needed
for the next invoice and is stored per journal.  (so we have a chain of hashes)

Tests written by Simon (smdc)

Part-of: odoo/odoo#124901