WIP: sout: add tracing for stream_ouptuts

This MR implements automatic tracing (when a tracer is enabled) of stream out/filters input and is a continuation of the work of @nicolas_lequec on the core pipeline timestamps tracing.

There is still case by case work to do on sout modules that create sub streams, they probably need to allocate a different es track name and forward it to the next stream via pf_add.

I've put the MR in WIP mode because I'm not sure if it should contain all the missing module specific code or if this could be added on subsequent MR's.

However a review on the current way of implementing the tracing in sout is welcome as the currents commits are unlikely to change.