Mastodon queue can be stuck by ffmpeg jobs.

If a job uses more than 1 minute CPU time, it's reasonnable
to consider we can skip it.

Meanwhile, regular and legitimate ffmpeg jobs are useful to extract
thumbnails for video and complete in some seconds.

This change provisions an utility to kill ffmpeg jobs
to Sidekiq containers if they spend more than one minute CPU time.

Ref T1492.

Script has been tested with succes on the Nasqueron instance.

Unit tests are provided with a data sample taken from production.