Add sink for Spinnaker

This has come up a few times as a data source from which people want to store data in InfluxDB. Thanks to @darinfisher pointing this out, it looks like this [integration could be written in Python](https://github.com/spinnaker/spinnaker-monitoring/tree/master/spinnaker-monitoring-daemon/spinnaker-monitoring). I thought about creating a feature request in Spinnaker repo but thought I'd post here first to get some thoughts/discussion on it.

I would look into contributing it myself but my quarter is full. May look into it Q4 if not picked up by then.

Start with the linked Spinnaker monitoring path and review how this repository handles integrations that store monitoring data in InfluxDB. Clarify the sink's scope, data flow, configuration, and acceptance criteria with maintainers before choosing implementation files. Done would require an agreed design and a working Spinnaker-to-InfluxDB integration.

Written by the indexing model from the issue text.