Allow to set audio/video device id that is used for testing

[szymonkups]

First of all - thanks for the great library.

I would like to propose a functionality that will allow setting audio and video device id that will be used during connectivity test. The reason is that sometimes participants happen to have more than one video/audio input devices installed in their system. Often (especially on Windows) happens that some of the devices are broken. We provide a device picker before the network test, where users can pick a working device and we would like to test using those picked devices.

I would be more than happy to implement this by myself and create PR. Looking forward to any guidance from the maintainers. My initial idea was to add second optional parameter (object with audioDeviceId and videoDeviceId optional string fields) to NetworkTest.testConnectivity() that will be passed down to testConectivity() -> checkPublishToSession -> checkCreateLocalPublisher. In checkCreateLocalPublisher i would validate if provided devices are part of availableDevices and use those ids as an audio/video source.

[miksansegundo]

@szymonkups here is what I did: #106