Terragrunt support

[lanmalkieri]

Really love the look of this tool, I think it has a ton of overlap with a tool like terragrunt, however I still see a few things I personally would really love to see in something like astro before I fully switched off terragrunt, a few off the top of my head:

• automatic backend creation (terragrunt supports creating s3 & dynamo tables for you)
• terragrunts ability to source parent directories allowing a single file to define global environment variables.

Rather than implementing the same type of features terragrunt supports today, I am wondering how big of a lift it would be to just support the terragrunt binary in astro itself. Basically combine the functionality of the two tools and use astro around terragrunt for the benefits of both.