Enhancement: Control EULA with environment variable

[CourteousCoder]

Summary

It would be great to set the EULA with an environment variable (with a sensible default of false). This way anyone who uses this docker image can accept or decline the EULA before starting up the container and can freely change their mind later.

I suggest adding an environment variable called EULA that defaults to the empty string, and replacing these lines with the following:

echo "eula=${EULA:-false}" > eula.txt

A nice bonus is that this solution might also fix some issues related to running this with something like Kubernetes. I was using Rancher to manage my Kubernetes cluster, and when I first fired up papermc, I had to bring it down just to edit the eula.txt manually.