Add estimated data rate to InfluxDBPublisherAgent

[BrianJKoopman]

After seeing recent issues with InfluxDB keeping up with published data, it would be useful to have some estimate of how much data is being published to InfluxDB.

This could be published to a feed and recorded for display in Grafana, however the Agent can't subscribe to its own feeds. One way around this would be to just directly insert the data into the queue that published data is recorded to. Some of the info passed here will need to be "made up" in a sense, as it won't actually be a real feed.