Analyse EventContext.version constraints #999
Description
As discovered in #998, the version field in the EventContext was set to required, while it is actually allowed to be null in the EventFactory.
The only real example of the valid null version is currently the import event flow. Even though it is valid for import event, for the general event processing flow it is not.
In order to bring the proper constraint for the version field back more investigation and analysis work required.
One of the probable solutions may be having a oneof with a version or smth else for import event flow.
Also, while the version is not required anymore, there should be an additional check somewhere in the storage that ensures that null or default version is never stored.