Switch to Azul Zulu.

The Alpine Zulu 15-jre Docker image is much smaller than the OpenJDK
15-slim image (65 MB vs. 200 MB), which is a good enough reason to
switch to it.

Change-Id: Ibde104f6f4217b06af756e842e45f07e243509db
diff --git a/src/main/resources/application.properties b/src/main/resources/application.properties
index 088e4e0..87f49c8 100644
--- a/src/main/resources/application.properties
+++ b/src/main/resources/application.properties
@@ -84,8 +84,8 @@
 quarkus.container-image.name = mulkcms2
 quarkus.container-image.registry = docker.benkard.de
 
-quarkus.jib.base-jvm-image = openjdk:15-slim
-#quarkus.jib.jvm-arguments = -XX:+UnlockExperimentalVMOptions,-XX:+UseShenandoahGC,-XX:ShenandoahGCHeuristics=compact
+quarkus.jib.base-jvm-image = azul/zulu-openjdk-alpine:15-jre
+#quarkus.jib.jvm-arguments = -XX:+UseShenandoahGC,-XX:ShenandoahGCHeuristics=compact
 
 quarkus.native.container-runtime = docker