Add select credentials test vector with multiple Fields

[tomdaffurn]

In the test vectors for the Presentation Exchange "select credentials" feature, no test case has an Input Descriptor with more than one Field.
test-vectors/presentation_exchange/select_credentials.json

Add a new test vector that has an Input Descriptor with multiple Fields.

This is necessary to demonstrate a bug in the web5-go implementation of SelectCredentials. It might also be present in other language SDKs.

It will also exercise the AND relationship of multiples Fields in an InputDescriptor

[decentralgabe]

related to #171