Is your feature request related to a problem? Please describe.
Currently the only external metrics provider is Prometheus. It would be nice if additional providers were added to the project.

Describe the solution you'd like.
Add support for querying metrics out of InfluxDB

Describe alternatives you've considered.
No other alternatives

Explain any additional use-cases.
The Sherpa API could be used in conjunction with Kapacitor, but having native support in Sherpa to query InfluxDB is very convenient.

Additional context.
Add any other context or screenshots about the feature request here.