event emission: implement generic event reporting gRPC client

#10407 added proto definitions for a generic event reporting service. This issue tracks implementation details.

1. Using a bidi stream where Envoy updates the emission stream based on responses from the sink gRPC service allows for in-band flexibility. Both for:

• The types of events that Envoy emits, e.g, filter to only health check events.
• The shape of the events emitted, e.g, configure the metrics events to report counters as deltas.

2. The base implementation should account for generic logic, such as:

• Stream establishment, and callbacks for custom logic over messages in the stream
• Handling versioning of in-band config updates so that the server-side gRPC service is aware of the configuration of the data stream -- useful when the shape of the data can change via in-band config updates.

Relates to https://github.com/envoyproxy/envoy/issues/8970 and https://github.com/envoyproxy/envoy/issues/10968