[OID4VP] Implement AuthorizationEndpoint logic in the Swift SDK

[yshyn-iohk]

Proposed feature

This issue is a subtask of the hyperledger-identus/.github#16

The SDK should be able to receive the Authorization Request from the Verifier, process it, compose the VP token, and post it to the Verifier.

Feature description

Implement all the logic after the Authorization Request is received. The wallet should perform the following tasks after scanning the QR code:

1. Parse the Authorization Request URI
2. Fetch the Authorization Request Object from request_uri in the Authorization Request
3. Fetch Presentation Definition from presentation_definition_uri in the Authorization Request Object
4. Evaluate the Presentation Definition and construct a VP token
5. Submit a VP token using HTTP POST to response_uri in the Authorization Request Object

[yshyn-iohk]

Moved back to the repository backlog.