Be able to automatically use correct Java version

[SpraxDev]

I believe the official java-setup action sets env vars for all installed java versions. Otherwise some auto-detection might be possible too making it usable in non GitHub Actions environments.

Detecting the recommended Java version could be done the same way BuildTools does - By fetching the build info for the requested version manually first and then launching BuildTools with that recommended version (if available).

With this you would be able to just install Java 8,11,17 and tell this project to compile the given Spigot versions and handle the details.