Document DID Prism resolution changes in the Identus Platform v2.15

[yshyn-iohk]

In the Identus Platform v2.15, the cloud agent uses the short form of the DID prism in the issuance and verification flows.

To facilitate the transition, the corresponding documentation should be created:

1. How to resolve DID Prism in SDK
2. List the endpoints of the DID resolution
3. DID resolution using the cloud agent