Add environment variable for --runtime-interface-emulator-address

At the moment it's not possible to configure the runtime interface emulator address without patching the docker image.

The default is `0.0.0.0:8080` , and I would like to restrict it to the local network for security reasons.

Start by locating the --runtime-interface-emulator-address flag definition and the code that applies its default of 0.0.0.0:8080. Done means an environment variable can configure the address without patching the Docker image, including restricting it to a local network address.

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