GH-3026: Fix chmod support for DSL

Fixes https://github.com/spring-projects/spring-integration/issues/3026

**Cherry-pick to `5.1.x`**

* Populate proper `FileTransferringMessageHandler` impl from DSL spec
implementations.
This way we are able to use a provided `chmod` from Java DSL
* Added `FileTransferringMessageHandlerSpec` ctor TODO
* Update SftpTests
* Code cleanup; `@Ignore` `SftpTests.testSftpOutboundFlowWithChmod()`
since it doesn't work properly on Windows

spring-integration-ftp/src/test/java/org/springframework/integration/ftp/dsl/FtpTests.java

@@ -66,6 +66,7 @@ import org.springframework.util.FileCopyUtils;
 /**
  * @author Artem Bilan
  * @author Gary Russell
+ * @author Joaquin Santana
  *
  * @since 5.0
  */
@@ -192,6 +193,30 @@ public class FtpTests extends FtpTestSupport {
 		registration.destroy();
 	}
 
+	@Test
+	public void testFtpOutboundFlowWithChmod() {
+		IntegrationFlow flow = f -> f
+				.handle(Ftp.outboundAdapter(sessionFactory(), FileExistsMode.FAIL)
+						.useTemporaryFileName(false)
+						.fileNameExpression("headers['" + FileHeaders.FILENAME + "']")
+						.chmod(0644)
+						.remoteDirectory("ftpTarget"));
+		IntegrationFlowRegistration registration = this.flowContext.registration(flow).register();
+		String fileName = "foo.file";
+		Message<ByteArrayInputStream> message = MessageBuilder
+				.withPayload(new ByteArrayInputStream("foo".getBytes(StandardCharsets.UTF_8)))
+				.setHeader(FileHeaders.FILENAME, fileName)
+				.build();
+		registration.getInputChannel().send(message);
+		RemoteFileTemplate<FTPFile> template = new RemoteFileTemplate<>(sessionFactory());
+		FTPFile[] files = template.execute(session ->
+				session.list(getTargetRemoteDirectory().getName() + "/" + fileName));
+		assertThat(files.length).isEqualTo(1);
+		assertThat(files[0].getSize()).isEqualTo(3);
+
+		registration.destroy();
+	}
+
 	@Test
 	@SuppressWarnings("unchecked")
 	public void testFtpMgetFlow() {