Auto update AWS nodes on new release

[jasny]

Allow nodes on AWS to automatically update when a new release is published.

Docker Hub to AWS SNS

• Setup a webhook in Docker Hub
• The webhook will trigger an AWS Lambda function (via API gateway?)
• Lambda triggers an AWS SNS notification.
  • Anyone should be able to subscribe to the SNS topic.

CloudFormation

When deployed using our CloudFormation template, a node should automatically update. Only update if there is a new version of the tag specified in as cloudformation parameters.

Example: if the v1.6 tag is chosen, only update if the v1.6 tag is updated (eg with v1.6.5). Don't do anything when v1.7.0 is released.