Make buyer electronic address configurable

[barredterra]

We currently use the email address as the buyer electronic address (BT-49). For reliable addressing in Peppol, we need to make this configurable.

Current:

<ram:URIUniversalCommunication>
    <ram:URIID schemeID="EM">mail@example.org</ram:URIID>
</ram:URIUniversalCommunication>

eu_einvoice/eu_einvoice/european_e_invoice/custom/sales_invoice.py

Lines 327 to 328 in 81599f3

	if self.invoice.contact_email:
	self.doc.trade.agreement.buyer.electronic_address.uri_ID = ("EM", self.invoice.contact_email)

eu_einvoice/eu_einvoice/european_e_invoice/custom/sales_invoice.py

Line 296 in 81599f3

self.doc.trade.agreement.seller.electronic_address.uri_ID = ("EM", electronic_address)

Desired:

<ram:URIUniversalCommunication>
    <ram:URIID schemeID="ANY_SCHEME">ANY_ADDRESS</ram:URIID>
</ram:URIUniversalCommunication>

Add two fields in Customer and Company:

• E Invoice Address Scheme (Link to Common Code, filtered by appropriate Code List)
• E Invoice Address (Data)

Fetch these into the Sales Invoice and use them in XML generation.

The relevant code list is "Participant Identifier Schemes" available at https://docs.peppol.eu/edelivery/codelists/