Add Labels and Environment variables to universe packages

[a-nldisr]

By default every Service has the ability to use environment variables and labels, great for those of us who use this feature to enable/disable certain services such as Marathon-LB, Traefik, Hashicorp Vault, opt in for monitoring to mention a few. While Universe packages usually have none of these options unless specifically tailored to the applications needs.

Currently we are using Marathon to work around this issue, since marathon is no longer actively developed it would be nice if DCOS had these values by default in all Universe packages. We now have to launch a service, edit the marathon and redeploy.

Please let me know if this is the wrong place to put this, i image a template is used for new universe packages and there are some requirements before deploying a service. I believe allow using environment variables and labels should be part of it.