Support both string and JSON encoded variant of presentation_definition and dcql_query

[TimoGlastra]

An issue we've ran into with the DCQL implementation from the PR in credo is that it encodes the dcql_query as string. For presentation_definition it encodes it as JSON object when doing JAR.

I think the agreement for OID4VP is to use string when encoding as url query, but if using JAR we can keep it as json. When parsing we should support both to increate interoperability.

See openid/OpenID4VP#378

@auer-martin could you take this into account with the oid4vp impementation?

[TimoGlastra]

Update: openid/OpenID4VP#422

[TimoGlastra]

Fixed in #21