Allow templates in OCI manifest names (Standardize Package Internals)

[Racer159]

Is your feature request related to a problem? Please describe.

As a package creator I want to have PKG_TMPLs in my manifest names so that I can better control what helm chart names are generated for my manifests.

Describe the solution you'd like

• Given I have a zarf.yaml with a manifest with a name set to a template (i.e. MY_NAME)
• And the package is published as a skeleton
• When I import that skeleton package into another package
• And run zarf package create --set MY_NAME=thename
• Then Zarf successfully creates the package with my name templated

Additional context

This would be easiest to fix by using the same layout as files and datainjections ('idx/filpath.Base()`) - we should also clarify how helm charts are named - it is a combination of package name component name and manifest name.

[Racer159]

Changed the title a bit since this may be a good opportunity to take a look at package internals and standardize things (like manifests) that don't match the norm - this should help put us on better footing for future feature implementation.