Add datasetItemsUpdate method to SDK

[jannikmaierhoefer]

Describe the feature or potential improvement

The TS SDK currently exposes datasetItemsCreate but provides no way to update an existing dataset item. Calling datasetItemsCreate with an existing id does not overwrite or modify the item.

A dedicated datasetItemsUpdate function (or allowing create to upsert when an id is provided) would make it much easier to manage datasets programmatically, especially for workflows that iteratively refine or correct dataset entries.

Additional information

No response