chore(refactor): packager warnings to be a proper type or struct

[lucasrod16]

Describe what should be investigated or refactored

refactor packager warnings to be a proper type or struct

Links to any relevant code

https://github.com/defenseunicorns/zarf/blob/22f2598e33dc28e91ed8609bbfb6b134113b2f9f/src/pkg/packager/common.go#L41

Additional context

https://github.com/defenseunicorns/zarf/pull/2223#discussion_r1492886244

cc: @Noxsios

[AustinAbro321]

I think we'll probably want to combine at least some of the warnings with the lint / validator. I believe we already have some duplicated logic in the lint code anyway