make getRequestedCredentialsForProofRequest more in line with other methods

[TimoGlastra]

the getRequestedCredentialsForProofRequest in the proofs module currently expects an indy proof request as input. We should abstract such details away as much as possible.

Current

const retrievedCredentials = await aliceAgent.proofs.getRequestedCredentialsForProofRequest(
  indyProofRequest!,
  presentationPreview
)

Proposed

const retrievedCredentials = await aliceAgent.proofs.getRequestedCredentialsForProofRequest(
  proofRecord.id
)

OR below

but as modules mostly take ids I think the first is better. The service could then take a record.

const retrievedCredentials = await aliceAgent.proofs.getRequestedCredentialsForProofRequest(
  proofRecord
)