Add /devices.json to extract devices informations

[tomamplius]

add uri like /devices.json to extract devices values with the bellow structure :+1:

{
"Device name" : {
    "device attribute" : "attribute value",
    ......
 },
 .....
}

Sample :

{

  "Luminosité Salon": {
    "battery": 71,
    "illuminance": 29269,
    "illuminance_lux": 845,
    "last_seen": 1660398470374,
    "linkquality": 204,
    "power_outage_count": null,
    "voltage": 3100
  },
  "volet_salon": {
    "last_seen": 1660398364946,
    "linkquality": 105,
    "position": 0,
    "state": "ON"
  },
  "volet_cuisine": {
    "color_mode": "xy",
    "last_seen": 1660398402975,
    "linkquality": 105,
    "position": 0,
    "state": "ON"
  },
  "sun": {
    "altitude": 4.67863705624236,
    "azimuth": 2.59147035508098,
    "time": "13:48",
    "date": "22-08-13"
  }
}