Add OnEnableEventHandlerChanged event

refs #5219
Add On{Check,Retry}IntervalChanged event

refs #5219
Add On{Event,Check}CommandChanged event

refs #5219
Add OnMaxCheckAttemptsChanged event

refs #5219
Add OnCheckPeriodChanged event

refs #5219
Modify OnVarsChanged event to pass values

refs #5219
Add cluster api events for modified attributes support

refs #5219
Merge branch 'feature/mod-attr-cluster-5219'

fixes #5219