INT-4095: Support Limiting (S)FTP Files Fetched

JIRA: https://jira.spring.io/browse/INT-4095

Limit the number of remote files fetched on each poll (when it is necessary to fetch files).

Polishing - PR Comments

Polishing - Decouple MaxFetchSize from Poller

Polishing - PR Comments

Schemas and Docs

More Polishing

* Polishing according PR comments

spring-integration-sftp/src/test/java/org/springframework/integration/sftp/config/InboundChannelAdapterParserTests-context.xml

@@ -42,6 +42,7 @@
 								  temporary-file-suffix=".bar"
 								  comparator="comparator"
 								  local-filter="acceptAllFilter"
+								  max-fetch-size="42"
 								  delete-remote-files="${delete.remote.files}"
 								  preserve-timestamp="true">
 		<poller fixed-rate="1000">

spring-integration-sftp/src/test/java/org/springframework/integration/sftp/config/InboundChannelAdapterParserTests.java

@@ -102,6 +102,7 @@ public class InboundChannelAdapterParserTests {
 		Collection<FileListFilter<?>> filters =
 				TestUtils.getPropertyValue(source, "fileSource.scanner.filter.fileFilters", Collection.class);
 		assertThat(filters, hasItem(acceptAllFilter));
+		assertEquals(42, source.getMaxFetchSize());
 		context.close();
 	}
 
@@ -117,6 +118,7 @@ public class InboundChannelAdapterParserTests {
 				.getPropertyValue(autoChannelAdapter, "source.synchronizer.remoteDirectoryExpression", Expression.class)
 				.getExpressionString());
 		assertSame(autoChannel, TestUtils.getPropertyValue(autoChannelAdapter, "outputChannel"));
+		assertEquals(Integer.MIN_VALUE, TestUtils.getPropertyValue(autoChannelAdapter, "source.maxFetchSize"));
 		context.close();
 	}
 

spring-integration-sftp/src/test/java/org/springframework/integration/sftp/inbound/SftpInboundRemoteFileSystemSynchronizerTests.java

@@ -137,7 +137,7 @@ public class SftpInboundRemoteFileSystemSynchronizerTests {
 		assertNull(nothing);
 
 		// two times because on the third receive (above) the internal queue will be empty, so it will attempt
-		verify(synchronizer, times(2)).synchronizeToLocalDirectory(localDirectory);
+		verify(synchronizer, times(2)).synchronizeToLocalDirectory(localDirectory, Integer.MIN_VALUE);
 
 		assertTrue(new File("test/a.test").exists());
 		assertTrue(new File("test/b.test").exists());