feat: Add rescheduleOrCreate method to the SchedulerClient

[beilCrxmarkets]

feat: Add rescheduleOrCreate method to the SchedulerClient

When invoking SchedulerClient.reschedule() with a non-existent TaskInstance, an exception will be raised. Therefore, it's essential to verify the existence of a scheduled TaskInstance prior to attempting a reschedule. To streamline this process, we propose the introduction of a scheduleOrCreate method. This method would automatically schedule a TaskInstance if none exists, making it particularly beneficial for dynamically recurring tasks that require initial setup.

We have given considerable thought to finding an appropriate name for this method, but unfortunately, we haven't arrived at a satisfactory conclusion. The verb "schedule" best describes its functionality; however, it cannot be used as there is already a method with that name. Since "rescheduleOrSchedule" sounds awkward, we have settled on "rescheduleOrCreate" for now. We are open to considering other names for this method.

Fixes

#539

Reminders

• Added/ran automated tests
• Update README and/or examples
• Ran mvn spotless:apply

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cc @kagkarlsson