Event stream partitioning.

[jmalloc]

The current event stream API does not allow specification of a stream within an application. It is assumed that every application has exactly one stream (as is the case with Verity).

We need to support multiple streams per application. This could be done by adding an additional piece of information to the API - a "partition ID" or "stream ID".

Another approach would be to simply rename "application ID" to "stream ID" within the consume request. Verity would simply use the application as the stream ID, whereas Veracity would be free to expose multiple streams with other IDs.

Regardless of the approach taken, the event stream API will need a way to enumerate the available streams.

There may also be a requirement to include "site" information in the API.

[jmalloc]

A new gRPC API has been added to enginekit. No site related functionality has been added (and may not be necessary in this API, not sure yet).