Add support for provisioning Greengrass devices for DockerApplicationDeployment connectors

[NickDarvey]

Docker containers running as a Connector need to be configured as a Greengrass device in order to communicate with other Greengrass components or AWS IoT over MQTT topics.

Use case

I have a Docker container which does object recognition that I want to run on the edge. I want to be able to publish events straight onto a MQTT topic to AWS IoT without needing 'companion' Lambda function.
Right now I can deploy most of the things I need using GGP, however this scenario currently requires manual steps including provisioning certificates and keys.

Usage

I'd like to declare my Docker connector's MQTT comms in my .conf in a manner similar to a Lambda function, e.g. fromCloudSubscriptions, toCloudSubscriptions (or is it inputTopics, outputTopics?) and have GGP provision a device, generate a bootstrap setup that includes installing certificates and keys for the device to a known or configurable location, and provisions subscriptions based on my configuration.

(This is based on what I understand of GGP, which is limited. If a different model of usage would fit better with GGP's design, please feel free to revise.)

References

https://docs.aws.amazon.com/greengrass/latest/developerguide/docker-app-connector.html#docker-app-connector-mqtt-communication