Fix(BREV-2357): CloudCredId in nebius cloud

[dishankj-max]

1. Previously, when retrieving Nebius instances, the CloudCredRefID field was always set to the current client's credential ID (c.refID), not the ID of the credential that was originally used to create the instance.
2. When creating an instance, we now store the creator's cloud credential ID in a new cloud-cued-ref-id label in the instance metadata
3. When converting Nebius instances back to v1 format, we extract the cloud-cred-ref-id from the instance labels instead of using the current client's ID
4. Backward compatibility - For instances created before this change (without the cloud-cred-ref-id label), the code falls back to the current client's ID with a warning log