Explicit/Unified filters for All Event Sources #1267

For v3 the PrimaryToSecondaryMapper was removed. However the idea was that user can do filtering events in SecondaryToPrimaryMapper and we would add more explicit event filters and related APIs if requested. But since now a caching mechanism is added to be able to remove PrimaryToSecondaryMapper, filtering events could mean in some cases that the indexing is not happening for the secondary resource. Basically if the resource is not mapped to a primary it is not added to the index (although the goal was just to filter out the event)
That's why there should be no filtering in SecondaryToPrimaryMapper but we should introduce explicit filters for events for provided event source implementations.