Introduce OpenBSD cron ~ notation

[jmettraux]

     A random value (within the legal range) may be obtained by using the `~'
     character in a field.  The interval of the random value may be specified
     explicitly, for example "0~30" will result in a random value between 0
     and 30 inclusive.  If either (or both) of the numbers on either side of
     the `~' are omitted, the appropriate limit (low or high) for the field
     will be used.

[andrew-solomon-oleeo]

This would be a welcome feature to avoid spike in load on cicd servers:

https://forum.gitlab.com/t/pipelines-with-random-schedule/86076