Support server event streams (#1479)

* Support server event streams
* Rename EventStreamInput to EventStreamSender
* Custom event stream errors
* EventStreamSender and Receiver are parametrized also on event stream error types
* Pokemon service model updated
* Pokemon server event handler
* Pokemon client to test event streams
* EventStreamDecorator to make optional using SigV4 signing
* Use forInlineFun for all errors

Closes: #1157

Signed-off-by: Daniele Ahmed <ahmeddan@amazon.de>

Co-authored-by: John DiSanti <jdisanti@amazon.com>