Seperate schemes for VP/VCI, make custom uri support ecosystem decision

[jogu]

closes #239
closes #240
closes #248

[awoie]

I believe this is missing:

# IANA Considerations

## Uniform Resource Identifier (URI) Schemes Registry

This specification registers the following URI scheme
in the IANA "Uniform Resource Identifier (URI) Schemes" registry [@IANA.URI.Schemes].

### haip-vci

* URI Scheme: haip-vci
* Description: Custom scheme used for invoking wallets with credential offers implementing the OIDF HAIP profile
* Status: Permanent
* Well-Known URI Support: -
* Change Controller: OpenID Foundation Digital Credentials Protocols Working Group - openid-specs-digital-credentials-protocols@lists.openid.net
* Reference: (#xxx) of this specification

### haip-vp

* URI Scheme: haip-vp
* Description: Custom scheme used for invoking wallets implementing the OIDF HAIP profile
* Status: Permanent
* Well-Known URI Support: -
* Change Controller: OpenID Foundation Digital Credentials Protocols Working Group - openid-specs-digital-credentials-protocols@lists.openid.net
* Reference: (#xxx) of this specification


<reference anchor="IANA.URI.Schemes" target="https://www.iana.org/assignments/uri-schemes">
  <front>
    <title>Uniform Resource Identifier (URI) Schemes</title>
    <author>
      <organization>IANA</organization>
    </author>
    <date/>
  </front>
</reference>

[Sakurann]

wg discussion:

• noting that this change means that there is no mechanism in HAIP that will always get Credential Offer and openid4vp request from issuer/verifier into the wallet.
• current direction is to keep credential offer mandatory, but say that ecosystems/trust frameworks etc. need to define a way to "reliably" get Credential Offer and openid4vp request from issuer/verifier into the wallet.
• "if you support an external invocation, credential offer must be supported/becomes possible"
• Wallet has a right not to use credential offer for non-technical reasons...

[Sakurann]

i believe above changes would also resolve #241 ?

[jogu]

Discussed on EU WG call today, consensus to merge this once the IANA section updated (even though it's not been open a week) to allow us to publish a new numbered draft soon.

[jogu]

i believe above changes would also resolve #241 ?

I'm not sure it does, or at least I didn't think this PR changed anything in the area of same/cross device flows.

Discussed with Oliver over signal; he's not able to review right now but was happy for us to proceed now the IANA considerations are there.