Enable configuration of PORT and SSL_PORT

[rahearn]

For our use-case, we need to be able to listen on port 8080 instead of 9000. This change enables that while leaving default behavior almost completely unchanged.

• Existing use cases of docker run -p 9000:9000... will continue to work unchanged
• Anyone using docker run -P to automatically map container ports to random host ports will need to add --expose=9000 --expose=9443 to their command to maintain the same behavior.

If we were running entirely in docker, we could have done this with -p 8080:9000 but our environment actually unpacks the docker image and repacks it in another buildpack, so we can't use the -p flag and instead have to rely on $PORT

[rahearn]

Converting this to draft as I work out some issues with this implementation with our provider.

[mogul]

We should probably leave the defaults in there and override them with the content of the env vars only if they're present. That will also maintain existing behavior in the binary for cases where the port hasn't been specified in the environment previously.