Credential-Issuance triggered by the RP

[philpotisk]

We need to fix the once working flow to onboard a user and issuer a VC in the scope of credential verification. The flow got broken due to the update of the various SIOP specs for credential exchange.

In the scope of this task we should:

• [x] Analyze the changes in the protocol and implement the corresponding updates.
• [x] Update the demo that starts at: https://verfier.walt.id