chore: move cmd/common to cmd

[mkcp]

Describe what should be investigated or refactored

Right now the cmd package subpackage cmd/common containing shared functionality. Packages with overly-general names like common, utils, etc. are generally discouraged. We can make the system more maintainable by lifting the common package up into cmd and, if necessary, moving specific functionality to subpackages named after what hey provide. (viper.go looks like a good candidate for this).

Links to any relevant code

https://github.com/zarf-dev/zarf/tree/main/src/cmd/common

Additional context

Blocked by #3183, #2773

[mkcp]

Blocked by #3183, #2773