[FEATURE] multiple outputs for track egress (to generate thumbnails)

[shift-tyson]

Is your feature request related to a problem? Please describe.
I want to generate a thumbnail image for my recordings. With participant egress I can have multiple outputs:

`
const outputs = {
file: fileOutput,
images: imageOutput,
};

const egress = await egressClient.startParticipantEgress(roomName, participantId, outputs);
`

But for startTrackEgress, I can only specify a single output.

Describe the solution you'd like
I would like to be able to generate images for my track the same way it works for participant egress.

Describe alternatives you've considered
ffmpeg

Additional context