Add support for AWS Firehose

[pugnascotia]

I am writing a service that uses the AWS SDK to send requests to Firehose. I would like the AWS support in the agent extended to support Firehose. While I could write my own middleware, it looks like the necessary framework is already in place to add support for another AWS service, particularly an HTTP based one.

[CAVAh]

This question refers to the AWS SDK v3, I also need this.