feat: support cosign signatures / attestations and discover in zarf prepare find-images

[mjnagel]

Description

Output from @rjferguson21 and my dash day's explorations of this.

This PR includes:

• Logic pulled from cosign tree to detect and include signatures/attestations when using zarf prepare find-images
• Skips SBOMs and caching for "non-images" by checking layer mediatypes at pull time

Several TODOs for follow-on work based on the issue/other needs:

• Add in SBOM pulling when available, skip over syft creation of SBOM when applicable.
• Mutating digests as needed - in order for tools to identify the signature the tag for it must be tagged <digest>.sig. When zarf does its AddImageAnnotation this could change the image digest, making it so that the signature is no longer at the correct tag. Images already having that annotation are unaffected (which is why this works OK for Ironbank).

Related Issue

Relates to #475

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

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[Racer159]

I know it is still draft but figured I would add some initial comments

[Racer159]

It would be good to also update the fuzzy image regex to this while you touch the find images code:

["|=]([a-z0-9\-.\/:]+:[\w.\-]*[a-z\.\-][\w.\-]*)"

Welcome feedback on whether it makes sense and the full context is here: https://kubernetes.slack.com/archives/C03B6BJAUJ3/p1696639896292219?thread_ts=1696585484.114289&cid=C03B6BJAUJ3 (edited)

[Noxsios]

lgtm now the error was handled