test

Add flatten-maven-plugin for Sonatype Central Portal #1321

Job	Run time
test (JDK 21)	5m 16s
test_docker (zipkin-storage-elasticsearch)	8m 50s
test_docker (zipkin-collector-kafka)	1m 47s
test_docker (zipkin-collector-rabbitmq)	1m 11s
test_docker (zipkin-server)	3m 6s
test_docker (zipkin-collector-activemq)	1m 12s
test_docker (zipkin-storage-cassandra)	5m 16s
test (JDK 25)	4m 38s
test_docker (zipkin-collector-pulsar)	1m 43s
test_docker (zipkin-storage-mysql-v1)	1m 18s
	34m 17s

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