bench(asr-worker): perform load testing

[ClemDoum]

In order to avoid discovering our system at large scale the first time we'll need it, perform load testing at moderately large scale to assess:

• if scaling works properly
• end-to-end RTF (with temporal overhead, preprocessing, machine provisioning and so on): "how many hours does it take to transcribe end-to-end X hours of audio"
• cost