Add seed-parameter to Chat Completions API for reproducible output support

Thinking about this more, should there be a $options=[] parameter in that function instead of us adding this $seed and whatever else is added at a later date to the API?

Lets take this change in now, and consider API changes for the future. I agree it could be better formed.

Note that the parameter is in for developers, but future issues need to add support for this for the ECA integration and potentially other areas.

Automatically closed - issue fixed for 2 weeks with no activity.