Multi-arch support when downloading and caching assets

[pacostas]

This PR supports multi-arch in below ways:

• It generates a cache directory, based on the platform and the architecture of the requested target.
• It downloads the assets based on the naming convention repo-tag-paltform-arch, hence it fixes the issue downloading wrong asset in case of a multi-arch repo
• It support backward compatibility, so in case a repo is not multi-arch, it fallbacks to the previous behavior, which is downloading the first asset in the array.

[pacostas]

@ForestEckhardt Can you please take a look?

[pacostas]

@ForestEckhardt Should we move this repo under paketo buildpacks? (This question is unrelated to this PR)