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/scripts/run-all.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# Regenerates every file under docs/output/. Nothing in this module's documentation, or in the
+# article it accompanies, is typed by hand.
+#
+#   scripts/run-all.sh
+set -euo pipefail
+cd "$(dirname "$0")/.."
+mkdir -p docs/output
+
+mvn -B test > /tmp/awaitility-run.log 2>&1 || { cat /tmp/awaitility-run.log; exit 1; }
+grep -E 'Running |Tests run:|BUILD ' /tmp/awaitility-run.log > docs/output/00-full-test-run.txt
+echo "wrote docs/output/00-full-test-run.txt"
+echo "the rest of docs/output/*.txt is written by the tests themselves (see Capture.java)"