Relax DID validation on prover_did on a credential request

[ianco]

Prover DID can be any did, for example did:peer:

"prover_did": "did:peer:2.Vz6MksjZKAGZbiZvWaXucPoxTpRa6U2QgaqvbrzPq9A2Kcwpu.SeyJpZCI6IiNkaWRjb21tLTAiLCJ0IjoiZGlkLWNvbW11bmljYXRpb24iLCJwcmlvcml0eSI6MCwicmVjaXBpZW50S2V5cyI6WyIja2V5LTEiXSwiciI6W10sInMiOiJodHRwOi8vaG9zdC5kb2NrZXIuaW50ZXJuYWw6ODAzMCJ9"

This currently fails validation, and should pass.

The prover_did doesn't need to be a DID at all, so we could potentially remove this validation completely.

See hyperledger/aries-cloudagent-python#2714

[swcurran]

The validation is in anoncreds-rs? Ah…interesting.

[TimoGlastra]

The code is here: https://github.com/hyperledger/anoncreds-rs/blob/main/src/data_types/cred_request.rs

[swcurran]

@assigned to @andrewwhitehead -- a high priority one to get completed and into a release.