Add @LongRunningTest JUnit 5 condition

* Add docs about `@LongRunningTest`

src/reference/asciidoc/testing.adoc

@@ -168,12 +168,18 @@ The `org.springframework.integration.test.support` package contains various abst
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/AbstractRequestResponseScenarioTests.html[`AbstractRequestResponseScenarioTests`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/AbstractResponseValidator.html[`AbstractResponseValidator`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/LogAdjustingTestSupport.html[`LogAdjustingTestSupport`] (Deprecated)
-* https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/LongRunningIntegrationTest.html[`LongRunningIntegrationTest`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/MessageValidator.html[`MessageValidator`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/PayloadValidator.html[`PayloadValidator`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/RequestResponseScenario.html[`RequestResponseScenario`]
 * https://docs.spring.io/spring-integration/api/org/springframework/integration/test/support/SingleRequestResponseScenarioTests.html[`SingleRequestResponseScenarioTests`]
 
+[[test-junit-rules]]
+==== JUnit Rules and Conditions
+
+The `LongRunningIntegrationTest` JUnit 4 test rule is present to indicate if test should be run if `RUN_LONG_INTEGRATION_TESTS` environment or system property is set to `true`.
+Otherwise it is skipped.
+For the same reason since version 5.1, a `@LongRunningTest` conditional annotation is provided for JUnit 5 tests.
+
 ==== Hamcrest and Mockito Matchers
 
 The `org.springframework.integration.test.matcher` package contains several `Matcher` implementations to assert `Message` and its properties in unit tests.
@@ -220,6 +226,8 @@ assertThat(channel.send(message), is(false));
 ----
 ====
 
+
+
 [[test-context]]
 === Spring Integration and the Test Context
 

src/reference/asciidoc/whats-new.adoc

@@ -26,6 +26,13 @@ Also Kotlin lambdas now can be used for handler and source methods.
 
 See <<functions-support>>.
 
+[[x5.1-LongRunningTest]]
+==== `@LongRunningTest`
+
+A JUnit 5 `@LongRunningTest` conditional annotation is provided to check the environment or system properties for the `RUN_LONG_INTEGRATION_TESTS` entry with the value of `true` to determine if test should be run or skipped.
+
+See <<test-junit-rules>>.
+
 [[x5.1-general]]
 === General Changes