Add authenticated Docker registry for AWS Staging and Prod
Add authenticated Docker registry for AWS Staging and Prod

We enabled authenticated puppet docker registry for the AWS Integration
environment. This is to mitigate against the new Docker limits on
docker pulls for anonymous/unpaid accounts.  This has been successful
and will now be deployed to staging and production environments.

Tested by:
1. creating a private repo on docker hub and trying with puppet having installed this PR.

Ref:
1. [Trello Card](https://trello.com/c/M3zyF5kM/3898-identify-govuk-components-and-jenkins-jobs-which-pull-images-from-docker-hub-investigate-an-option-to-enable-authentication-for)

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet