support proxy mode

[scareything]

This is a placeholder for now. Not sure if this makes sense for the tunneler SDK, or if ziti-prox-c should continue to hold the "proxy" torch.

[qrkourier]

A member of the community suggested a use case for a proxy mode in forum this topic.

[qrkourier]

It may or may not apply to a future implementation of a proxy mode for ziti-edge-tunnel, but I hit an unexpected limitation in the Go tunnel proxy where I couldn't bind an arbitrary port when allowed ports was specified in the client config.

[qrkourier]

@scareything Can we name it run-proxy to extend the pattern of modes named like run*, e.g., run, run-host? I ask because the Docker entrypoint script currently looks for a first positional param named like run*.