Add support for check-alive using Meross plug power consumption reading

[whatUwant]

Fixes https://github.com/kiwi-cam/homebridge-broadlink-rm/issues/700

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Adding support for "ping" / check-alive capability using Meross smart plug's power consumption measurement. Tested plug models: MSS310 & MSS315.

Accessory UUID & user key can be obtained via the Meross plugin https://github.com/bwp91/homebridge-meross

Configuration:

"pingUseMeross": true,
"pingExtraConfig": {
  "merossAccessoryUuid": "PASTE_ACCESSORY_UUID_HERE",
  "merossUserKey": "PASTE_USER_KEY_HERE",
  "wattageThreshold": 10
}