Fix: Logging of delete by tag and copying descriptors

[sudo-bmitch]

Fixes issue

Debug logging of a tag deletion does not show the tag annotation.

Describe the change

The descriptor was not copied, resulting in the deletion from the index overwriting the descriptor that was being logged. This fixes the Index.GetDesc call to always return a copy, and it fixes the copy to clone the annotations. This also improves the testing around GC.

How to verify it

go run ./cmd/olareg serve --port 5002 --store-type mem -v debug --gc-frequency 2m --gc-grace-period 5m --api-delete --gc-untagged &
regctl image copy localhost:5000/regclient/regctl:alpine localhost:5002/regclient/regctl:alpine
regctl tag rm localhost:5002/regclient/regctl:alpine
# view the logs of the deleted descriptor

Changelog text

• Fix: Logging of delete by tag and copying descriptors

Please verify and check that the pull request fulfills the following requirements

• Tests have been added or not applicable
• Documentation has been added, updated, or not applicable
• Changes have been rebased to main
• Multiple commits to the same code have been squashed