Add support for server-side events and tests

User can POST to web endpoint in SSE style, i.e:

HTTP/1.1
Content-Type: text/event-stream

data:foo

data:bar

Will be converted to a Flux with values foo and bar

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamConfiguration.java

@@ -38,6 +38,7 @@ import reactor.core.publisher.Flux;
 @EnableBinding(Processor.class)
 @EnableConfigurationProperties(FunctionConfigurationProperties.class)
 @ConditionalOnClass({ Binder.class, AbstractFunctionInvoker.class })
+@ConditionalOnProperty(name = "spring.cloud.stream.enabled", havingValue = "true", matchIfMissing = true)
 public class StreamConfiguration {
 
 	@Autowired