Rename 'running' to 'ready' for ApplicationStartup

Rename 'spring.boot.application.running' to
'spring.boot.application.ready' to better align with `ReadinessState`.

Closes gh-28080

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java

@@ -79,7 +79,7 @@ void started(ConfigurableApplicationContext context, Duration timeTaken) {
 	}
 
 	void ready(ConfigurableApplicationContext context, Duration timeTaken) {
-		doWithListeners("spring.boot.application.running", (listener) -> listener.ready(context, timeTaken));
+		doWithListeners("spring.boot.application.ready", (listener) -> listener.ready(context, timeTaken));
 	}
 
 	void failed(ConfigurableApplicationContext context, Throwable exception) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java

@@ -1173,7 +1173,7 @@ void customApplicationStartupPublishStartupSteps() {
 		verify(applicationStartup).start("spring.boot.application.context-prepared");
 		verify(applicationStartup).start("spring.boot.application.context-loaded");
 		verify(applicationStartup).start("spring.boot.application.started");
-		verify(applicationStartup).start("spring.boot.application.running");
+		verify(applicationStartup).start("spring.boot.application.ready");
 		long startCount = mockingDetails(applicationStartup).getInvocations().stream()
 				.filter((invocation) -> invocation.getMethod().toString().contains("start(")).count();
 		long endCount = mockingDetails(startupStep).getInvocations().stream()