[FEATURE] Add support for Jenkins-style 'H' hashed field value

[dmayle]

As mentioned in the wikipedia on cronspecs, Jenkins supports a new field value 'H' (or 'H/15', etc.) which is used to specify a random stable offset within the schedule. Jenkins hashes (hence the 'H') the job name to to allow you to give the same schedule to multiple jobs without running into the thundering herd problem.

In order to support this, the API would need to change to allow passing in a job name to use for hashing.

This would make it easier to schedule recurring jobs on kubernetes.

[dmayle]

Interestingly enough, #307 is a feature request for adding a job name.

[alokpr]

I need to schedule hundreds of jobs with similar schedule, where this feature will be immensely useful.

[sean-]

Any updates to this issue? Top-of-the-hour thundering herd is an easily preventable problem. I would love to change @hourly to H * * * * * where H renders to the hash of the Job Name, PID, hostname, or something pseudo-random. Or, instead of H, R for random.

[adampetrovic]

I've sent up a PR for this, though it looks like the repo has stopped being maintained for quite some time.

#531