[INCREMENTAL] Introduce Support for Pressure, PM1.0, and PM4.0 Custom Characteristics

[rhockenbury]

    // TODO: Not supported by HomeKit yet.
    // this.absolutePressureSensor = new OccupancySensor(
    //   platform,
    //   accessory,
    //   "Absolute Pressure"
    // );
    // this.relativePressureSensor = new OccupancySensor(
    //   platform,
    //   accessory,
    //   "Relative Pressure"
    // );

Previously implemented as occupancySensors, can potentially wait for better support for pressure characteristics in HomeKit or re-implement using the occupancySensor.

Outdoor and indoor pressure is reported by various Ecowitt devices.

These can be implemented via a Motion, Occupancy or Contact sensor (along with custom characteristics) to implement a threshold for automation.

[rhockenbury]

• custom service - Custom services not displayed homebridge/homebridge#2740
• service definition - https://github.com/homebridge/HAP-NodeJS/blob/8804db59230b4fc8e2d4a2f9971ea05a3def28d2/src/lib/definitions/ServiceDefinitions.ts#L891
• char definition - https://github.com/homebridge/HAP-NodeJS/blob/8804db59230b4fc8e2d4a2f9971ea05a3def28d2/src/lib/definitions/CharacteristicDefinitions.ts#L2085