feat(state): define property to set forwarder connection state

Signed-off-by: rgallor <[email protected]>

io.edgehog.devicemanager.ForwarderSessionsState.json

@@ -0,0 +1,16 @@
+{
+  "interface_name": "io.edgehog.devicemanager.ForwarderSessionsState",
+  "version_major": 0,
+  "version_minor": 1,
+  "type": "properties",
+  "ownership": "device",
+  "description": "This property is set by a device to provide information about the status of a remote terminal session.",
+  "mappings": [
+    {
+      "endpoint": "/%{session_token}/status",
+      "type": "string",
+      "description": "Indicates if the device is connecting, connected or disconnected to a remote terminal session.",
+      "doc": "An enum with the following possible values: Connecting | Connected | Disconnected."
+    }
+  ]
+}