Add metrics to sensors in device

[oscgonfer]

Add simple statistics on the device > data > sensors to be used for various purposes, testing or informative. These metrics can come from kairos directly and be:

• count (top prio)
• mean
• max
• min
• std
• count null (????)

[pral2a]

Minor comment. As this data will require a read on Kairos for every metric, should we add a flag to the request to enable it?

[oscgonfer]

Makes sense!