- Add PUPPET_AUTH_TOKEN support for authenticating with private gem source
- Add comprehensive RSpec tests to verify gem source configuration
- Constrain Puppet version to 8.11.x when using private source with no version
- Add gem_name parameter to location_for for smarter source selection
- Maintain backwards compatibility with public source

Signed-off-by: Gavin Didrichsen <gavin.didrichsen@gmail.com>