[WIP][ADD] accounting/l10n_es: documentation for new Veri*Factu module

[svfu-odoo]

Spain introduces a new EDI called "Veri*Factu" to send all invoices to the Spanish tax agency (AEAT). It is mandatory for most tax payers (that cannot use any of the other Spanish EDIs like SII or TicketBAI)

In the related community PR new modules were added to enable sending invoices and PoS orders via "Veri*Factu".

This commit adds some documentation about how to enable and use "Veri*factu".

references

community PR: https://github.com/odoo/odoo/pull/197635 task-3745982

[robodoo]

[svfu-odoo]

Closed to not block the merge of the main PR I will open a dedicated PR later: https://github.com/odoo/documentation/pull/14086