Add analytics data

[ericzbeard]

We can record usage analytics by adding this to templates generated by Rain:

Metadata:
  AWSToolsMetrics:
    Rain: {string - whatever we want}

This will be recorded by the CloudFormation service.

This should be implemented by the deploy command, which will add the metadata node silently, unless the user specifies the --no-analytics flag.

Data to record:

• Rain version
• Modules used? This would be hard, since modules could be local paths, uris, zipped packages. It's not like CDK with standard libraries. If we do this, it will have to be done by the pkg command too.
• Features used? Modules, metadata

Maybe the version is all we need?

Design the data model to be flexible in case we want to add new elements later. Maybe a base64 encoded and compressed yaml string.

Next question is, if all we add is the version, what does this give us over existing analytics based on SDK calls with the user agent?