Move the asr-metrics dependencies into a 'extra' set of dependencies

[JamesG-Speechmatics]

Installing numpy and other large libraries is not necessary if only doing realtime speech recognition. This MR moves the dependencies of asr_metrics into a larger version of the package to be installed as

pip3 install speechmatics-python[full]

todo: code in asr_metrics to fail gracefully on import error.

Because this is a breaking change for anyone who does use asr_metrics, the major version is bumped from 2 to 3.