Improve API Documentation for Anoncreds

https://discord.com/channels/905194001349627914/1252629630763012116/1420415377212571648

The documentation for creating an Anoncreds Presentation Request is currently incomplete and somewhat misleading. The example payload shown in the [tutorial](https://hyperledger-identus.github.io/docs/tutorials/credentials/didcomm/present-proof)
does not align with what the API actually expects in release v2.0.0.

Issues identified:

Missing proofs field
The request body must include a top-level proofs attribute (an array), even if it is empty.
Without this field, the API returns:

400 RequestBodyDecodingFailure (missing at 'proofs')

This requirement is not mentioned in the tutorial, so users following it will consistently encounter this error.

Incorrect cred_def_id format
The documentation shows cred_def_id as a simple identifier (e.g. 3fc80ccf-d8da-3215-a626-8712f73d5101).
In practice, the API requires a full URL to the credential definition, such as:

${agent.url}/credential-definition-registry/definitions/${anoncredGuid}/definition

Without the correct format, proof requests cannot be resolved.

Recommendation:
The API and Swagger docs should clearly define the expected formats for cred_def_id, schema_id, and other fields. This would make error messages (such as Bad Request) more meaningful and significantly reduce confusion for developers.