fix: use $JAVA_OPTS in decoder4u (#1030)

following #964

Author: c-dilks

bin/decoder4u

@@ -6,7 +6,7 @@ split_cli $@
 
 export MALLOC_ARENA_MAX=1
 
-java -Xmx2304m -Xms1280m -XX:+UseSerialGC ${jvm_options[@]} \
+java ${JAVA_OPTS-} -Xmx2304m -Xms1280m -XX:+UseSerialGC ${jvm_options[@]} \
     -cp ${COATJAVA_CLASSPATH:-''} \
     org.jlab.detector.decode.CLASDecoder4U \
     ${class_options[@]}