[Improvement] Support multi-tag identifiers in TagEvent

### What would you like to be improved?

`ListMetadataObjectsForTagsEvent` class has a design limitation when handling multiple tags. The event is constructed to work with multiple tag names but must use a single `NameIdentifier` due to the `TagEvent` parent class design.

Originally mentioned in https://github.com/apache/gravitino/pull/7476#discussion_r2203742316

### How should we improve?

The current workaround is to use the first tag as the identifier when constructing the event. We'd like to find a way to redesign the tag event system to support multiple tags as identifiers in order to represent all tags involved in an event.

cc @FANNG1