Remove support for publishing packages as `artifact.manifest` mediatypes

[Noxsios]

Describe what should be investigated or refactored

The OCI spec has removed the artifact.manifest spec in favor of using the image.manifest for everything due to registry support and there not being a good enough reason to have another entire spec. opencontainers/image-spec#999

As such, Zarf should remove support for this, as very few registries support artifact.manifest anyways and none will support in the future.

[Noxsios]

Refactoring the manifest's image config should also take place in this PR: #1434

[Racer159]

This is blocking us from updating oci spec and crane - we could pull these local like oras did but might as well rip off the bandaid.

[Noxsios]

Bandaid ripped w/ ceb6da1 @Racer159

[Noxsios]

closed by #1469