Represents a user of the proxy for an electronic invoicing format.
    An edi_proxy_user has a unique identification on a specific format (for example, the vat for Peppol) which
    allows to identify him when receiving a document addressed to him. It is linked to a specific company on a specific
    Odoo database.
    It also owns a key with which each file should be decrypted with (the proxy encrypt all the files with the public key).
    