Upgrading to Java 25 for newer server versions (26.x) #56

Hello @TheRemote and contributors,
Setting the minecraft server version to 26.x is currently broken due to the newer Java requirements:

Minecraft 26.1 and newer requires running the server with Java 25 or above. For information on how to update Java, see https://docs.papermc.io/misc/java-install

Looking at the Dockerfile, would it be reasonable to always fetch the latest OpenJDK major version instead of hardcoding it?
It might not always be ideal and could cause breakage, but using a predetermined version also exposes users to potential vulnerabilities. Also, it might reduce your need to match Java versions to each release in the future (although that's a bit rare)

Or, if feasible, allow the user to set a specific OpenJDK version since their naming is usually the same with openjdk-{{var}}-jre-headless, although im not sure if that'd work.

Thank you!