Switch to more named errors (particularly in src/pkg)

[Racer159]

Describe what should be investigated or refactored

We should prefer to use named errors in future features and should look through the code for places that we can standardize errors to be specific instantiations.

Links to any relevant code

https://github.com/defenseunicorns/zarf/blob/main/src/pkg/packager/create.go#L108

Additional context

This would help us be a better library to others and would help with unit tests.

[Noxsios]

imo this issue is too broad in scope + not very actionable.

Moving to defenseunicorns/pkg for a bit so the team is aware + can include this mentality as we build out the design docs for those libraries.