New user/verifier task - Request Claim

[RieksJ]

Requirement: It MUST be possible for verifiers to construct a request for data that they need in order to produce a particular result, such as, but not limited to, a decision.

Motivations: One of the core problems that we try to solve is to enable verifiers to use data that it doesn't have itself, but is readily and electronically available from other parties. Knowing what data is available from which issuers is covered by #138. Using information from such claim offers may, however, not be sufficient to (a) create a request for such a claim and (b) validate the response, i.e. determine that the data provided in the response is valid for processing as the verifier intends (where 'valid' means that if the result of such processing is incorrect, or comes with a risk for the verifier that it finds unacceptable, that is not because of (the contents of) that claim.