Include a Definition of an ARM Template

I logged an [issue](https://github.com/Azure/azure-sdk-for-go/issues/333) against the azure-sdk-for-go, but they pointed me here.

The generated SDK does not define a type that represents an ARM template. It can be approximated based on existing types (mostly), but it would be better to a have a definitive way to represent one.

Start by reviewing the linked azure-sdk-for-go issue and the existing generated types that approximate an ARM template. Determine the required definitive representation and its scope; the issue is done only when the repository provides a clear, agreed-upon ARM template type.

Written by the indexing model from the issue text.