Add awaitility module: testing async @Async/@Scheduled/@KafkaListener code without Thread.sleep

Covers replacing Thread.sleep with await() across a void @Async method, an
@EmbeddedKafka-backed @KafkaListener, and an already-running @Scheduled job;
verifies Awaitility 4.3.0's real defaults (10s timeout, 100ms poll interval)
and its default-uncaught-exception-handler swap directly against the jar;
and documents a real pom.xml trap where Boot 4.1.1 split Kafka's
autoconfiguration (spring-boot-kafka) out of spring-kafka itself, which
silently leaves @KafkaListener beans with no running container.

awaitility/docs/output/10-missing-kafka-starter-failure.txt

@@ -0,0 +1,23 @@
+== Real failure with org.springframework.kafka:spring-kafka as a direct dependency instead of org.springframework.boot:spring-boot-starter-kafka (pom.xml since fixed) ==
+
+$ mvn -B test
+[ERROR] Errors:
+[ERROR]   KafkaListenerAwaitTest.messageSentIsEventuallyConsumed:49 ? ConditionTimeout Assertion condition defined as a Lambda expression in com.ankurm.awaitility.KafkaListenerAwaitTest
+Expecting ConcurrentLinkedQueue:
+  []
+to contain:
+  ["order-42-created"]
+but could not find the following element(s):
+  ["order-42-created"]
+ within 5 seconds.
+[INFO]
+[ERROR] Tests run: 11, Failures: 0, Errors: 2, Skipped: 0
+
+No exception at context startup, and the application context came up without a single warning.
+Autowiring KafkaListenerEndpointRegistry directly in a scratch test and calling
+getListenerContainers() on it confirmed the real cause: the bean did not exist. Neither did
+KafkaTemplate, ConsumerFactory, or kafkaListenerContainerFactory. Grepping the full log for the
+Spring Kafka logger prefix also confirmed it:
+
+$ grep -c "o\.s\.k\." full-test-run.log
+0