Fix non-OK HTTP POST responses handling (#374)

Currently, JDK HttpClient SSE implementation incorrectly handles a
non-2xx HTTP response code for POST. Instead of immediately failing the
caller, it ignores the issue and the user awaits until the timeout kicks
in.

Set HttpClient to use HTTP/1.1 version explicitly for tests

A related problem happened with the WebClient Streamable HTTP
implementation, where the error was swallowed for non-400 responses.

Signed-off-by: Dariusz Jędrzejczyk <dariusz.jedrzejczyk@broadcom.com>