INT-4284: Integration Properties @Bean => static

JIRA: https://jira.spring.io/browse/INT-4284

Prevent early instantiation of config.

spring-integration-core/src/test/java/org/springframework/integration/gateway/GatewayInterfaceTests.java

@@ -543,7 +543,7 @@ public class GatewayInterfaceTests {
 	public static class TestConfig {
 
 		@Bean(name = IntegrationContextUtils.INTEGRATION_GLOBAL_PROPERTIES_BEAN_NAME)
-		public Properties integrationProperties() {
+		public static Properties integrationProperties() {
 			Properties properties = new Properties();
 			properties.setProperty(IntegrationProperties.READ_ONLY_HEADERS, IGNORE_HEADER);
 			return properties;