GET /credentials endpoint should return result object instead of an array

[PatStLouis]

The GET /credentials endpoint is currently set to return an array of credentials. I would suggest to instead return an object with a results property containing an array of credentials to enable pagination.

[msporny]

The group talked about this on the 2024-12-17 telecon:

@PatStLouis noted that the return value should be an object instead of an array. For all endpoints we return an object, which return results and can provide other metadata with the result, pagination support, etc. The results keyword was suggested as the top-level object property name.

This is ready for PR, there were no objections to the path forward.