Add ECR user creds as env vars in CircleCI project settings for injection

[timshoaf]

We don't want to be storing secrets as plaintext so we will have them injected at build time into our CircleCI build container for use in pushing the generated docker artifacts to ECR.

We need to add all of

          account-url: AWS_ECR_ACCOUNT_URL_ENV_VAR_NAME
          aws-access-key-id: ACCESS_KEY_ID_ENV_VAR_NAME
          aws-secret-access-key: SECRET_ACCESS_KEY_ENV_VAR_NAME
          region: AWS_REGION_ENV_VAR_NAME

[timshoaf]

Done.