identify method
Update user properties using operations provided via Identify API.
To update user properties, first create an AMPIdentify object.
Example: if you wanted to set a user's gender, increment their karma count by 1, you would do:
final Identify identify = Identify()
..set('gender','male')
..add('karma', 1);
Amplitude.getInstance.identify(identify);
Implementation
Future<void> identify(Identify identify) async {
Map<String, dynamic> properties = _baseProperties();
properties['userProperties'] = identify.payload;
return await _channel.invokeMethod('identify', jsonEncode(properties));
}