Nginx configuration parameters as environment variables

[obermeier]

With the new modules extensions-all-jvm and extensions-iiot-minimal the nginx configuration should be updated to be able to use the HTTP-Server adapter the established way.

Since the hostname of the service could differ (extensions-all-jvm, extensions-iiot-minimal, ...), what do you think of the idea of adding an option to set the host via an environment variable.
The current ui docker image contains the tool envsubst which is able to set the values in the nginx configuration.

A short example: Link