Implement DID Document Structure and update storage

[juanmagiraldor]

Objective

Implement DID Document struct and update storage.

Checklist

1. Implement DID Document Struct:
   • Create a robust DIDDocument struct to comprehensively represent Decentralized Identifiers (DIDs) along with their associated information.
2. Revise Storage to Save Only a DID Document:
   • Modify the storage mechanism to exclusively store a single DIDDocument for each Decentralized Identifier.
   • Ensure that the storage design aligns with the updated DIDDocument structure.
3. Reflect All Changes in the DID Document:
   • Ensure that any modifications or updates in the contract, particularly related to DIDs, are accurately and consistently reflected in the associated DIDDocument.
4. Return DID Document in All Functions:
   • Modify existing functions to return the updated DIDDocument after any operations.
   • This ensures a cohesive and straightforward approach, providing a complete snapshot of the DID Document post-function execution.

[miguelnietoa]

Implemented and available at v0.2.0