In order to differentiate between event types, we need to know internally whether or not an event came from externally or from Camunda. Using the properties of an event alone doesn't provide this option. We should therefore use the source field to determine this. Camunda events already use the value camunda for this field, so we should also prevent this being used for ingested external events.
Hint: If any existing events have been ingested with that value, we might need to assist with helping customers update their values (would also be part of various other indices, so could be complex)
- Ingested events cannot use camunda as the value of the source field
- The upgrade documentation mentions this breaking change