Implement a helper method to iterate sinkpads

Try to push it to GstElement?
Add loggin around AGGREGATE locking
TaskFunction returns nothing
Set all pads as flushing in a first pass to guarantee we do wait for the *last* flush_stop to forward it
PAUSE the srcpad task on actual FLUSH_START and push the FLUSH_STOP serialized

+ FIX the test as we are now actually pushing flush_stop in the srcpad
thread
Properly stop/start all pads when going to PAUSE/READY
Check if flushing before and after waiting for buffer consumption on the pad

Also do not concider we are EOS for the buffer that came in before we received EOS ... this one is good to go.
Properly lock + update cookie when stopping the streaming thread
Take the Aggregate lock when looking at flush stop on pads.

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