Feature Request: Provide ECR Hosted Image

[gjtempleton]

Our clusters make use of Gatekeeper and OPA to prevent deployment of pods making use of non-ECR hosted images.

Currently the k8s-cloudwatch-adapter image is only provided via Dockerhub, meaning that we have to mirror it to our internal ECR registry every time a new tag is published before we can make use of it.

It would be great and save us this toil if instead this could also be hosted on an AWS ECR registry for users to use.