Create Verifiable Presentation and Verifiable Presentation Signing

[nitro-neal]

We need Verifiable Presentations to wrap our presentationSubmission. An example can be found here: https://identity.foundation/presentation-exchange/#presentation-submissions

Currently we have this (only presentationSubmission object, no VerifiablePresentation)

val presentationSubmission: PresentationSubmission = PresentationExchange.createPresentationFromCredentials(listOf(vcJwt2, vcJwt1), pd)

I suggest we change it to be like this:

val vp: VerifiablePresentation = PresentationExchange.createPresentationFromCredentials(listOf(vcJwt2, vcJwt1), pd)
val vpJwt = vp.sign(issuerDid)

The change to our existing codebase will be to:

• Create a VerifiablePresentation model object and
• update the createPresentationFromCredentials to construct a vp that has a presentationSubmission from the inputs it is given

[andresuribe87]

This makes sense to me!

[andresuribe87]

Just FYI, a related convo will happen in #176. Shouldn't be a blocker for this though.

[nitro-neal]

#184