RATIS-2629. Handle Netty based request asynchronously and improve exception handling

[spacemonkd]

What changes were proposed in this pull request?

RATIS-2629. Handle Netty based request asynchronously and improve exception handling

Currently NettyRpcService handles every inbound request synchronously on the Netty IO event-loop thread and its inbound handler does not override exceptionCaught.

This can cause:

• a slow or long-running request occupies the worker thread delaying all other requests on that event loop
• only IOException is converted into an error reply. Any other Throwable escapes the handler with no exceptionCaught, Netty's default handling only logs it and never writes a reply, so the client blocks until its request timeout.

This patch offloads the request handling out of the core IO path, and closes the channel to prevent blocking.
This mirrors how gRPC handles the requests.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-2629

How was this patch tested?

Patch was tested via unit tests.

[spacemonkd]

@szetszwo could you take a look?