feat: add support for nested template rendering

[micovery]

Up to now, you could only templetize the main file, or define helper functions.

This change makes it so that you can render any arbitrary file like this:

{{ include "./path/to/file.yaml" . }}

This is useful for dynamically generating policies without having to in-line them in the main template.

Also, add a --debug=true flag to help users troubleshoot template rendering