Re-consider the kafka ingress ordered delivery semantics

[slinkydeveloper]

In our kafka implementation we inherited much of the constraints about ordering from the delivery guarantees of the keyed/unkeyed service.

This is not needed anymore, and we should implement the following new semantics now:

• For Virtual objects with exclusive handlers, the kafka record key MUST be UTF-8 valid, and you get ordering on key basis.
• We forbid subscribing to Kafka Virtual objects with shared handlers. This is unclear how it should work, and what are the user expectations. Once it's more clear, we can allow it.
• For Services, we wanna support two delivery semantics:
  • Max fanout no ordering.
  • Ordering on topic/partition basis. For this we can profit from the recent changes to ids and service status/invocation status table split, to define on an invocation basis whether we wanna have ordering and on which key.