Assigning to helene.waechtler as it's probably something to consider when splitting/merging the process instance index

We currently have an events property of each process instance, which contains the FlowNodeInstanceDto}}s for a given instance. However, these DTOs are created from the {{FlowNodeEventDto, which has a confusing name as it has no relation to Optimize events. We should, at the least, rename the FlowNodeEventDto and it's subclass to something less confusing. In addition, it would be good to rename the events field of the process instance class