INT-4324: File Outbound: parse preserve-timestamp

JIRA: https://jira.spring.io/browse/INT-4324

The `preserve-timestamp` attribute for the
`<int-file:outbound-channel-adapter>` has been missed for parsing in
the `FileWritingMessageHandlerBeanDefinitionBuilder` and propagation
in the `FileWritingMessageHandlerFactoryBean`

**Cherry-pick to 4.3.x**

spring-integration-file/src/test/java/org/springframework/integration/file/config/FileOutboundChannelAdapterParserTests-context.xml

@@ -18,6 +18,7 @@
 								   directory="${java.io.tmpdir}"
 								   temporary-file-suffix=".foo"
 								   chmod="777"
+								   preserve-timestamp="true"
 								   filename-generator-expression="'foo.txt'"/>
 
 	<file:outbound-channel-adapter id="adapterWithCustomNameGenerator"

spring-integration-file/src/test/java/org/springframework/integration/file/config/FileOutboundChannelAdapterParserTests.java

@@ -146,6 +146,7 @@ public class FileOutboundChannelAdapterParserTests {
 		if (FileUtils.IS_POSIX) {
 			assertThat(TestUtils.getPropertyValue(handler, "permissions", Set.class).size(), equalTo(9));
 		}
+		assertEquals(Boolean.TRUE, handlerAccessor.getPropertyValue("preserveTimestamp"));
 	}
 
 	@Test