Support for Labels

[simplesteph]

It seems that docker-gen as of 0.4.0 supports placing some variables in labels instead of environment variables, which is a bit cleaner.

nginx-proxy/nginx-proxy#172 (comment)

Thoughts on implementing this?
I could try doing a PR at some point

[codesuki]

If you want to do that you have to read about docker labels here:
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_definition_parameters.html

We can access those parameters.

For me it would be low priority because it works fine with environment variables for now. I would prefer to add path (instead of domain) mapping and authentication first.