GH-841 Add support for propagating errors from AWS Custom Runtime

Resolves #841

spring-cloud-function-samples/function-sample-aws-custom/src/main/java/com/example/LambdaApplication.java

@@ -21,6 +21,9 @@ public class LambdaApplication
 	public Function<String, String> uppercase() {
 		return value -> {
 			logger.info("Processing: " + value);
+			if (value.equals("error")) {
+				throw new IllegalArgumentException("Intentional");
+			}
 			return value.toUpperCase();
 		};
 	}

spring-cloud-function-samples/function-sample/src/test/java/com/example/WebTestClientTests.java

@@ -19,12 +19,6 @@ public class WebTestClientTests {
 	@Autowired
 	private WebTestClient client;
 
-	@Test
-	public void words() {
-		client.get().uri("/words").exchange()
-			.expectStatus().isOk().expectBody(String.class).isEqualTo("[\"foo\",\"bar\"]");
-	}
-
 	@Test
 	public void uppercase() {
 		client.post().uri("/uppercase").body(Mono.just("foo"), String.class).exchange()