MINOR: Handle Flowable History Cleanup

[IceS2]

This PR aims to do two different things:

• First of all, it aims to provide a good default for keeping the flowable historic tables nice and tidy to avoid them growing way too much
  This is done by setting the following config, with the default being cleaning history of processes after 7 days they ended.

  processEngineConfiguration
      .setEnableHistoryCleaning(true)
      .setCleanInstancesEndedAfter(
          Duration.ofDays(
              workflowSettings.getHistoryCleanUpConfiguration().getCleanAfterNumberOfDays()));

• Second, it parametrizes the main configurations that should be defined depending on the different use cases
  This was done by setting a new SystemSetting: WorkflowSetting.
  The main thing I'm not sold on is how I'm updating the ProcessEngine after a setting change is done. I'd love any inputs since it seems it is the first time we are doing this.

Type of change:

• Improvement

Checklist:

• I have read the CONTRIBUTING document.
• My PR title is Fixes <issue-number>: <short explanation>
• I have commented on my code, particularly in hard-to-understand areas.
• For JSON Schema changes: I updated the migration scripts or explained why it is not needed.

[sushi30]

I suggest having a pub/sub mechanism in the SystemRepository allowing objects like the WorkflowHandler to listen to configuration changes. So postUpdate should call all the subscribers instead of explicit objects and WorkflowHandler can choose what to do with t he update based on the SettingsType. This will keep the dependency tree linear (SystemRepository -> WorkflowHandler). This might also be useful in the context of the Application framework.

But that can be done on another iteration.