Abort package install if JAVA_HOME is not set and java is not in the path

Since #28928 we create the keystore in a post-install script. Through our scripts, this requires that `JAVA_HOME` be set or that `java` is in the path. If this is not the case, the post-install script fails and the installation is broken. It is too late to be failing in post-install. Instead, we should add a check in pre-install for this and fail early.