Pleast add a way to test MPEG2 V4L2 decoder

[lumag]

Please implement GStreamerV4l2MPEG2Gst10VideoDecoder. The naive implementation does not work with the real world driver (venus).

[rgonzalezfluendo]

GStreamer implementation is here.

Adding support in fluster is not complicated, I'm sure Copilot will do it correctly. Unfortunately, we don't have any hardware to test it on.

If you could test it and confirm that it works, that would be great.

[lumag]

I've implemented and tested mpeg2 decoders for ffmpeg and Gstreamer. Waiting for the internal clearance before opening a PR.