Provide a mechanism to capture exceptions during request handling

[freshtonic]

Interceptors are insufficient for capturing errors in the general case because they execute after a request has already been successfully decoded.

This commit introduces a new concept called an ExceptionSink. It is a behavior that exposes an error/2 function.

ExceptionSinks are attached to an Endpoint like this:

defmodule EndpointWithExceptionSink do
  use GRPC.Endpoint

  exception_sink ExceptionSink1
  exception_sink ExceptionSink2, foo: 1

  run Server
end

An ExceptionSink receives the raised exception and a stack trace, allowing the developer to process/forward that information to the observability tool of their choice.

Exceptions that are caught before sending to the exception sinks are reraised so that the existing behaviour is preserved.

[lessless]

@tony612 can you please at this PR? this is a heavily needed feature and will make debugging much simpler. thanks

[tony612]

It looks good overall. I just wonder if we can implement this feature with only interceptors?