Acr Purge: Improve purge command to support untagged manifest cleanup independently

[estebanreyl]

Description:

The current implementation of the purge command introduces the --untagged flag, which enables cleanup of untagged manifests when a specific filter is applied. However, this behavior combines the cleanup of both tagged and untagged manifests, making it cumbersome to perform a cleanup of only untagged manifests.

Additionally, the date filters do not apply to untagged manifests, further complicating targeted cleanup operations.

Expected Behavior:

Allow users to clean up untagged manifests independently of tagged ones. Ensure that filters (such as date filters) can be applied or are more clearly documented as inapplicable to untagged manifests.

Suggested Improvement:

Introduce a dedicated flag or mode that enables exclusive cleanup of untagged manifests without requiring tagged filters. This would simplify the process and improve usability for users targeting untagged manifest cleanup only.