Provide ability for docker container to accept JVM options

[ncuster]

This would provide the ability for the user to optionally specify any number of runtime options to the JVM in the exporter's container. This is important for users that might want to set certain Springboot options, reduce the JVM footprint (e.g. setting a heap max), etc.

[ncuster]

By providing an ENV in the Dockerfile, and changing ENTRYPOINT to use bash/sh then the execution of the container can optionally supply any number of JVM command line arguments.

[markxnelson]

closing this one since we moived to golang impl