Data Index events streaming with kafka

This JIRA is intended for the tracking and analysis of the possibility of adding data index specific event streams for notifying the data index processed information changes.

As discussed in the task assigning meeting, see:

"C) Kafka stream "task created / updated events” exposed by dataIndex (RFE kogito)"

in the following document:

https://docs.google.com/document/d/1mIdQY4fmahVdi8l9LzyudEholK_4RFaDLuKr2ZeldNI/edit?usp=sharing

Analogous to the Subscriptions, the data index might expose kafka topics that produces the following events:

• UserTaskInstanceAdded
• UserTaskInstanceUpdated
• ProcessInstanceAdded
• ProcessInstanceUpdated

The information flow should work like this: e.g.

1. a UserTaskEvent arrives to the data-index
2. the event is processed like now and the corresponding information is stored in the data-index storage
3. e.g. a UserTaskInstanceAdded event is generated and delivered to a kafka-topic
4. third party application receives the UserTaskInstanceAdded event

The steps above are performed in a transnational manner pretty much like it happens at the kogito runtimes level.

Additionally, events corresponding to the domain objects information updates could also be exposed, however are not a priority for the task assigning work.