Fix deprecation warnings

* Use `MatcherAssert.assertThat()`
instead of deprecated `Assert.assertThat()`
* Use `IntegrationFlows.fromSupplier(Supplier)`
instead of removed `IntegrationFlows.from(Supplier)`
* Use `org.springframework.integration:spring-integration-test`
throughout the project for more testing utilities

basic/pom.xml

@@ -4,7 +4,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>org.springframework.integration.samples</groupId>
   <artifactId>basic</artifactId>
-  <version>5.3.0.RELEASE</version>
+  <version>5.4.0</version>
   <url>https://projects.spring.io/spring-integration</url>
   <organization>
     <name>SpringIO</name>