Drop incoming frames when queue builds up

krdp starts to build a queue when the encoder is running quicker than the client can decode.

Previous attempts tried to tweak our frame rate, but this has a long latency before it fixes itself.

Instead we can pause the encoder and drop/coallesce frames there without changing the frame rate from kwin -> encoder.

This keeps latency very fast.

Requires kpipewire kpipewire!277 (merged)