[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.

Start by reading build.gradle.kts, focusing on the Spotless Java version compatibility configuration. Verify the current build behavior with Java 21, then confirm that Gravitino compiles successfully on Java 21 without breaking the existing build configuration.

Written by the indexing model from the issue text.