Consider adding option to schedule with fixed rate in MonitoredJobs

[sleberknight]

Currently the MonitoredJobs infrastructure classes only allow scheduling jobs using a "fixed delay", i.e. the delay starts after on execution ends.

Should we consider adding an option to allow scheduling at a "fixed rate" as well?

I'm not sure where the best place to put this would be. At first glance I thought the best place might be MonitoredJob as well as in the builder inside MonitoredJobs. But, a downside is that this means some of the static registerJob methods in MonitoredJobs will never allow scheduling with "fixed rate" since they don't accept a MonitoredJob instance. Every one of the existing registerJob methods does accept a JobSchedule instance so that might actually be a better location to put this option, as well as in the builder inside MonitoredJobs.

So for example, maybe you have something like:

var schedule = JobSchedule.builder()
    .initialDelay(Duration.minutes(1))
    .intervalDelay(Duration.minutes(10))
    .executionType(ExecutionType.FIXED_RATE)
    .build();

I'm not "wed" to ExecutionType but definitely want it to be an enum and not a boolean.

Inside JobSchedule we should make the default be fixed delay to preserve existing behavior, such that creating a fixed rate job would require callers to opt-in to that behavior explicitly.

References:

• ScheduledExecutorService#scheduleWithFixedDelay
• ScheduledExecutorService#scheduleWithFixedRate