APP-6785: Allow different service host from webrtc host

[ethanlookpotts]

createRobotClient uses the host for both the service host and the WebRTC host. In the case of a machine running with a local config (not using the cloud config), these values can be different. By providing a way to override the service host, createRobotClient can connect to machines running with a local config.

This is not a breaking change because existing WebRTC configs will not have serviceHost specified.

This was tested by using the Vanilla example with the following config:

    machine = await VIAM.createRobotClient({
      serviceHost: "http://localhost:8080",
      host: "localhost:8080", // or the FQDN specified in config.nework.fqdn
      signalingAddress: '',
    });