[Improvement] Standalone MiniGravitino module

### What would you like to be improved?

Gravitino provider a MiniGravitino class to support integration tests.
But MiniGravitino depends on some libraries, for example, Jetty, jersey, etc.
If we directly use MiniGravitino class, it is much easier to throw the Java package into conflict.

### How should we improve?

I think split MiniGravitino class into standalone, a MiniGravitino module, and shadow depends Jar packages.