create-package should support multi arch buildpacks

[anthonydahanne]

create-package should support multi arch buildpacks

it should understand the targets entries in buildpack.toml

and then be able to only copy from linux/a(md|rm)64/bin to bin

Possible Solution

after calling pre package, move the proper files under bin/

Motivation

support occam testing fwk that calls pre-package this way:

https://github.com/paketo-buildpacks/occam/blob/main/packagers/libpak.go#L19

which is in turn used this way:

	libpakBuildpackStore := occam.NewBuildpackStore().WithPackager(packagers.NewLibpak())
	watchexecBuildpack, err = libpakBuildpackStore.Get.
		Execute("github.com/paketo-buildpacks/watchexec")