We need filter debugging for OpusCleaner

[ZJaume]

Specially when running complicated language pairs that may not be well supported and suffer a lot from filtering (like Chinese Traditional), we need a detailed description of how much data each filter discards.

[ZJaume]

Maybe something like this tee that counts lines at the beginning and at the end of each step. Or using enabling that tee option, then count each step size.

[evgenyrp]

We should save a JSON with stats, similar to how it's done in HPLT importer: https://firefoxci.taskcluster-artifacts.net/YyrMdgH-QHG75qptWf5xSQ/0/public/build/mono_v3_0.en.stats.json