Restart AppNet Relay on failure

[yinyic]

Summary

Restart AppNet Relay on failure

Implementation details

Configure Docker restart policy for AppNet Relay container so that it will be restarted by docker if it exits due to an error.
MaximumRetryCount is set to 0 to indicate that we are not enforcing a maximum count (reference)

Testing

New tests cover the changes: no

Tested with new ECS Agent and verified that AppNet Relay has correct restart policy configured

$ docker inspect 805d395608a5 | jq .[0].HostConfig.RestartPolicy
{
  "Name": "on-failure",
  "MaximumRetryCount": 0
}

Description for the changelog

Restart AppNet Relay on failure

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.