Separate out the JAVA_OPTIONS for the --dry-run

Allow different JVM options to be set for the JVM which does the `--dry-run` than the one which runs the server.

Comment from @jnehlmeier in https://github.com/eclipse/jetty.docker/issues/160#issuecomment-1708025155_

> If you go that route it would be great if the `JAVA_OPTIONS` used to run the server would be adjustable dynamically without rebuilding the image. Basically executing `java $JAVA_OPTIONS -jar start.jar ....` to start the server. This could be done by applying `sed` on the output of `--dry-run` to insert the `$JAVA_OPTIONS` variable. I mentioned something like that already in https://github.com/eclipse/jetty.docker/issues/151#issuecomment-1669270102 because of JPMS.