Use Verifiable Presentation as described in the Verifiable Credential Data Model

Currently in ICAM specification document, it is said that Gaia-X Self-Description documents are Verifiable Presentations following the W3C Verifiable Credentials Data Model, with multiple example such as in 6.1 and 6.6.

In 6.6, the Verifiable Presentation does not have a proof element, which makes it, according to the Verifiable Credentials Data Model, a Presentation rather than a Verifiable Presentation. Having a Presentation is unsafe as it does not bind the Holder to the credential emitted and anyone could juste use the same Presentation.

To avoid misuse of the specification, we should change this example in 6.6 and also specify in 6.4.9 that if the type is Verifiable Presentation, then at least one proof MUST be included. (The same as for the Verifiable Credential).

For Verifiable Presentation, the proof element should also integrate a challenge and/or domain to prevent replay attacks