workloads: add a new camera preview workload

Created by: joelagnel

This workload starts the camera app, waits for a few seconds and then starts data collection (trace, energy etc).

I also have a workload that starts the camera app after tracingStart, I call it 'cameraStartup' however I don't know how useful it is for upstream so I dropped it. cameraStartup was useful for me when I was debugging the time it takes from the start of the camera app to the first preview frame.

Signed-off-by: Joel Fernandes joelaf@google.com