Add OS monitoring (power, CPU, temperature)

[seriyps]

This adds optional periodical polling of 3 types of OS sensors:

• CPU load
• Radxa chip temperature (those are built-in)
• INA226 power sensor (to monitor power supply, eg, battery voltage and current) - it requires INA226 sensor to be installed to i2c, which is a bit advanced topic

All 3 are publishing OSD facts so can be used for some kind of warning widgets or to just display the value. All 3 are optional, can be enabled/disabled/configured in pixelpilot.yaml

• sensors
• readme
• auto-discovery
• OSD widgets

[zhouruixi]

Can hwmon_id: auto be used to implement automatic detection?

[seriyps]

@zhouruixi auto-discovery added

os_sensors:
  cpu: auto
  power: auto
  temperature: auto

[seriyps]

I tested it on a real hardware and added some fixes. Untill I add widgets, the contents can be viewed with

        {
            "name": "Debug",
            "type": "DebugWidget",
            "x": 50,
            "y": 100,
            "facts": [
                {"name": "os_mon.cpu.load_total"},
                {"name": "os_mon.cpu.load_iowait"},
                {"name": "os_mon.temperature", "tags": {"sensor": "thermal_zone0"}},
                {"name": "os_mon.temperature", "tags": {"sensor": "thermal_zone1"}},
                {"name": "os_mon.power.voltage"},
                {"name": "os_mon.power.current"},
                {"name": "os_mon.power.power"}
            ]
        },