Log when active streams reaches and drops below max concurrent streams (#974)
Log when active streams reaches and drops below max concurrent streams (#974)

Motivation:

Reaching max concurrent streams will cause frames on additional streams
to be buffered, and can therefore see increased latency. Observing this
is difficult.

Modifications:

- Log any changes in HTTP/2 settings, not just the initial settings
- Add a warning log when our active stream count matches max concurrent
  streams
- Add a notice log when our stream count drops below max concurrent
  streams

Result:

Better observability when we get close to max concurrent streams.
grpc/grpc-swift,grpc/grpc-swift,grpc/grpc-swift,grpc/grpc-swift,grpc/grpc-swift