acmesh-official#944 (comment)

Let's Encrypt employee said in the comments "we do see peaks at the beginning of minutes and even seconds; the finer-grained time randomization, the better."

This adds a random amount of sleep second before beginning the cron job. I considered reading from `/dev/urandom` and so on, but we aren't doing anything security critical here so I thought that just using the process number modulo 59 (the largest prime <= 60) should give decent variability across the systems. The starting hour and minute are already randomized during the installation.

`docker-compose` was removed in actions/runner-images#9692