Add JAVA_OPTS environment variable

[flouou]

Is your feature request related to a problem? Please describe.
I would like to add remote debugging java opts to the docker container, which need to go between "java" and "-jar" in the beginning of the startup command.

Describe the solution you'd like
I think a solution would be to add "JAVA_OPTS" to the environment variables and place it betweed "java" and "-jar" in the docker-entrypoint.sh

Describe alternatives you've considered
An alternative would be to use a custom entrypoint script, which I did not really get to work for me (container did not start, even with copied standard entrypoint script.

Additional context
I am using felixklauke/paperspigot:1.14.4

Example debug options: -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005

If you have any other possible solutions on how to add debug options for remote debugging, please let me know!