Update azul/zulu-openjdk-alpine Docker tag to v21

Author: renovate[bot]

Dockerfile

@@ -1,3 +1,3 @@
-FROM azul/zulu-openjdk-alpine:17
+FROM azul/zulu-openjdk-alpine:21
 COPY build/libs/consumer-0.0.1-SNAPSHOT.jar app.jar
 ENTRYPOINT ["java","-jar","/app.jar"]