config option for JVM is needed

currently the charm ships with the default elasticsearch package, there are no viable options to configure the JVM tunables.
For e.g. on a larger deployment the default 2G heap size is insufficient.
One has to go to the /etc/elasticsearch/jvm.options and manually change Xms and Xmx to the desired value. Also the charm is not monitoring if the service is alive or not - always reports active, despite it is not running at all (due to Java heap space error).