Provide a way to configure which packages are copied and which not

**Describe the problem/challenge you have**
When relocating (imgpkg copy) a packagerepository that is old and has too many old versions into a new cluster/datacenter, we might know that old versions are never going to be used, so we want to blacklist them from copying over, so that size of images in destination repository and process of copying is improved.

**Describe the solution you'd like**
I would like to have a Config file that could have a blacklist/whitelist of packages that would be copied so that in the destination only the copied versions would exist and only the images for the specified package versions are copied.

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Start by reviewing the imgpkg copy workflow and how configuration is currently handled. Clarify the blacklist and whitelist semantics, including package versions and precedence, then define acceptance cases showing which images are copied and which are omitted from the destination repository.

Written by the indexing model from the issue text.