[Improvement] SchemaChange Support CommentChange

### What would you like to be improved?

We have a feature to modify the description information corresponding to the schema, but we found that Gravitino does not support the CommentChange type.

### How should we improve?

I want to know why we do not support the modification of comment information. Would it be difficult to implement this ourselves?

Start by locating the schema-change handling and CommentChange entry points in the Java project, since the issue names no files or tests. Trace how schema description changes are represented and handled, then determine the affected implementation and test locations. Done should mean comment modifications are supported and their behavior is covered by tests.

Written by the indexing model from the issue text.