Add Iceberg REST tests against Unity catalog

[denodo-research-labs]

After #24083, we should add tests against Unity catalog.

But we couldn't find any hosted container image. These pull request in the Unity project are paving the way to upload an image to Docker Hub: unitycatalog/unitycatalog#551 and unitycatalog/unitycatalog#698.
But using Docker Hub does not seem like a good idea as they are going to introduce limits on image pull and storage: https://www.docker.com/blog/november-2024-updated-plans-announcement/.

Another alternative could be to host a Unity container image in the GitHub Container Registry.

[tnightengale]

The tentative plan for the UC official image, is to host on DockerHub, but seek sponsorship for the project under the Docker-Sponsored Open Source Program. This should allow unlimited pulls of the forthcoming official image. We are working on getting this application approved, and an official image on DH asap.