Expose BluetoothGattCallback#onServiceChanged

[gabrielgarciagava]

Starting from API 31, there is a new method on the BluetoothGattCallback called onServiceChanged
https://developer.android.com/reference/android/bluetooth/BluetoothGattCallback#onServiceChanged(android.bluetooth.BluetoothGatt)

We need to know when this callback is called since it means the Gatt cache is out of sync and we need to rediscover the services by calling BluetoothGatt#discoverServices. Right now, when it happens, we cannot connect to the services anymore and it is not possible to know why.

Place that should respond to this new callback: https://github.com/dariuszseweryn/RxAndroidBle/blob/master/rxandroidble/src/main/java/com/polidea/rxandroidble2/internal/connection/RxBleGattCallback.java#L38