Add new measurement backend based on powerjoular project

[joestubbs]

Since it is not clear that Scaphandre continues to be maintained, we should explore other backends. One option that appears to be well documented is Powerjoular: https://github.com/joular/powerjoular.

Our approach will be to create a separate container image for powerjoular and start it in a separate process, passing the PID it should monitor as part of the container command line arg.