[Improvement] build.gradle.kts should support compiling with Java 21

What would you like to be improved?

Many people will not have earlier versions of Java installed, and Gravitino should support compilation with more recent versions of Java. The reason why this isn't currently supported is due to Spotless Java version compatibility issues in the build.gradle.kts file, but that can be worked around.

How should we improve?

Allow Gravitino to be compiled on more recent versions of Java.