Allow choosing the deviceId for Camera

[RafaRuiz]

Describe the bug
When having 1 internal camera and one external camera, the expected results vary. I can't choose what camera to use.
While I could choose the camera I wanted on Twilio, because I only had to give its ID

To Reproduce
I'm doing:

  Future<void> _initAgora() async {
    try {
      await engine //
          .initialize(const RtcEngineContext(appId: _agoraId));

      await engine.enableVideo();
      await engine.setCameraCapturerConfiguration(const CameraCapturerConfiguration(cameraDirection: CameraDirection.cameraFront));
      await engine.startPreview();
      await engine.setClientRole(role: ClientRoleType.clientRoleBroadcaster);

    } catch(e) {
      print(e);
    }
  }

alternating with CameraDirection.cameraFront and CameraDirection.cameraRear

Expected behavior

Despite any third-party Android (probably iOS too) camera library can give us the current cameras we can use with its ID (as shown in the next screenshot, where IDs are "0" and "1"

With Twilio (for calling), or any third party camera library to preview, I could say the deviceId I wanted and that was granted.

Current Behaviour

• When using CameraDirection.cameraFront: as expected, it's working with my front internal camera

• When using CameraDirection.cameraRear: no camera, so there's no way I can choose my external webcam

Context
I've plugged the same external camera that Agora can't get from one tablet, into another tablet that has 0 internal cameras, and I was able to use it.

Solution
We should be able to get the available video devices on Android, get their ID, and be able to choose the camera ID we want the source from.

[plutoless]

@RafaRuiz thank you for the issue report. This is more related to our native android sdk design. let me confirm with our PM regarding this issue.

[plutoless]

@RafaRuiz i have just confirmed with our PM this will be included in sdk version 4.3.1. For further info feel free to contact our support team.