Adapt JWT-Credential format to VC-JWT

[OSchlienz]

Current Behavior

MIW currently is using enveloping and embedding proof.

Expected Behavior

only enveloping proof should be supported.

Steps To Reproduce

while issuing new credential as JWT.

@thackerronak

[thackerronak]

@OSchlienz I tested the latest code and found it supports enveloping proof while creating VC as JWT.