[Feature Request] Grafana Dashboard and Turner Signal collector

[CygnusHyoga]

Hi! I'm very happy to see a new project of Prometheus exporter for HDHomeRun :-)

I have two feature request:

• Add a Grafana dashboard to the repo for easy use of the exporter.
• It will be nice to add TunerSignalStrengthRatio, TunerSignalToNoiseRatio, TunerSymbolErrorRatio like https://github.com/mdlayher/hdhomerun_exporter/blob/master/collector.go

Thanks!