Add possibility to provide credential offer by reference via credential_offer_uri in QR code

[jtalir]

Currently, credential offer is passed by value in QR code. Since OpenID4VCI allows two possibilities of providing credential offer (by value and by reference) and specification slightly prefer later one ("When the Credential Offer is displayed as a QR code, it would usually contain the Credential Offer by reference due to the size limitations of the QR codes") some wallets can only accept credential offer by reference. It would be great to have possibility to generate QR code with URI containting credential_offer_uri parameter.

I can imagine simple selection choice in https://issuer.eudiw.dev/credential_offer_choice:

• (*) by value
• ( ) by reference