Add jam pack flag so that it outputs a single arch

[braunsonm]

Describe the Enhancement

This is a duplicate of paketo-buildpacks/libpak#330

Add a flag that takes in the expected target and then output the buildpack format for a single arch (i.e. older format). In addition, filter the metadata dependencies and only include those for the specified arch.

Possible Solution

--platform linux/amd64 - possibly allowing a list of platforms you would like

Motivation

Not every user will want to build multi-arch images.