Add gpuop-cfg list-images command for csv and clusterpolicy

[karthikvetrivel]

Description

Adds a gpuop-cfg list-images [csv|clusterpolicy] command to print all container images referenced in a GPU Operator ClusterServiceVersion or ClusterPolicy manifest. This supports gov readiness workflows where we need to quickly grab the full list of operand images.

The image-listing logic is extracted from the existing validate code into a shared internal/images package so both validate and list-images use the same source of truth. The validate behavior is unchanged.

Checklist

• No secrets, sensitive information, or unrelated changes
• Lint checks passing (make lint)
• Generated assets in-sync (make validate-generated-assets)
• Go mod artifacts in-sync (make validate-modules)
• Test cases are added for new code paths

Testing

# List images from helm-rendered ClusterPolicy
# (extract the ClusterPolicy document from helm's multi-resource output)
helm template gpu-operator deployments/gpu-operator \
    | awk '/^---/{if(found)exit}{if(/kind: ClusterPolicy/)found=1}{if(found)print}' \
    | gpuop-cfg list-images clusterpolicy --input /dev/stdin

# List images from bundle ClusterServiceVersion
gpuop-cfg list-images csv --input bundle/manifests/gpu-operator-certified.clusterserviceversion.yaml

Verified that gpuop-cfg validate clusterpolicy and gpuop-cfg validate csv behavior is unchanged, including -ubuntu22.04 os-tag appending for Driver and GPUDirectStorage during validation.