Support Java versions other than 15

[johannes-riecken]

I'm trying to fuzz a Java 18 project and have added steps to install Java 18 to the Dockerfile and adjusted the env vars in the build.sh. The logs in my storage repo still show that somewhere in the process the old Java gets used. The Github Action passes in spite of the error, which isn't ideal.

Would it be possible to upload a Docker image to base-builder-jvm for fuzzing with Java 18 or to detail the steps to do that in the documentation?

[asomov]

FYI, my PR failed