ci: use multistage container build to reduce image size

Author: kofemann

packages/tar/src/main/container/Dockerfile

@@ -1,6 +1,17 @@
+#
+# This container only created a minimalistic JVM runtime environment suitable for running dCache.
+#
+FROM almalinux:9-minimal as builder
+
+# Add JRE
+RUN microdnf -y install java-21-openjdk-devel java-21-openjdk-jmods binutils
+RUN jlink --compress=zip-6 --strip-debug --no-header-files --no-man-pages --add-modules java.base,java.compiler,java.instrument,java.logging,java.management,java.naming,java.security.jgss,java.transaction.xa,java.xml,jdk.jfr,jdk.security.auth,jdk.unsupported,java.desktop,java.sql,jdk.naming.dns,java.rmi,jdk.crypto.cryptoki --output /jlink-runtime
+
 
 # Minimalistic Java image
 FROM almalinux:9-minimal
+COPY --from=builder /jlink-runtime /jlink-runtime
+RUN ln -s /jlink-runtime/bin/java /usr/bin/java
 
 ENV DCACHE_INSTALL_DIR=/opt/dcache
 
@@ -19,7 +30,7 @@ RUN echo "dcache:x:994:1000::/home/dcache:/bin/bash" >> /etc/passwd
 RUN echo "dcache:!!:18438::::::" >> /etc/shadow
 
 # Add JRE
-RUN microdnf -y install java-21-openjdk-headless hostname which procps-ng tar gzip
+RUN microdnf -y install hostname which procps-ng tar gzip
 
 # Add dCache
 COPY maven /opt/dcache
@@ -54,7 +65,7 @@ RUN chown -R dcache:dcache ${DCACHE_INSTALL_DIR}/var /pool
 
 # add s3hsm for fake tape interraction
 RUN curl -s -L -o /tmp/s3hsm.tar.gz https://github.com/kofemann/s3hsm/releases/download/v0.1.0/s3hsm_0.1.0_linux_amd64.tar.gz
-RUN cd /usr/bin && tar xzf /tmp/s3hsm.tar.gz s3hsm
+RUN cd /usr/bin && tar xzf /tmp/s3hsm.tar.gz s3hsm && rm /tmp/s3hsm.tar.gz
 
 # the data log files must survive container restarts
 VOLUME ${DCACHE_INSTALL_DIR}/var