Merge similar metrics into single ones with labels.

[Cova]

Metrics like klipper_temperaturefan_speed, or klipper_temperaturesensor_temperature, should be using labels rather than uniquely named metrics. I have a bunch of printers with extra fans/thermistors in them in various places, and it is resulting in a very large number of metrics which mostly have empty values as that sensor only exists in a single machine.

I would much prefer just a klipper_temperature_sensor{sensor="*"} style of metric to work with.

[scross01]

Made some initial changes to address this in the metrics_with_labels branch.

[scross01]

Fixed in v0.7.0