Feature: URIs as path

[ahuffman]

As a user, I would like the ability to point to an upstream git repository URL or Kubernetes URI to use as a source file in my instructions file. I would like the tool to pull these files to a temporary location, and then perform overlays from the instructions file.

In case of a git repository, it would be nice to have the ability to additionally make an automatic commit/push once overlayed, but needs to be thought about since an end-user should also manually review the changes to ensure contents are as expected.

Kubernetes URIs would be nice to be able combine with the -s stdout option and direct the output into kubectl or other alternative manifest application tools.