Maxscale Workload Statistics By Server By readwrite available via REST API

Enable statistics on workload by Server, by Readwritesplit via Maxscale Rest API.

The usecase for this would be for:

1) Be able to get workload information that could be rendered in a realtime monitoring tool/solution
2) Be leveraged to in some sort of external monitoring process that could determine whether additional nodes should be added to scale (i.e. autoscale)

Some thought will need to be put into things like:

• Total Counts (by server by readwrite) - This would likely be easiest/fine for first release
• Reset Total Counts (this could allow someone to manually reset the count or reset it automated every 5/10/30 minutes)
• Some way to retrieve Counts for last 5,10,30,60 minutes/etc