docs: clarify dataset fields consistency across dataset versions in API guide #11573

Added a note explaining the constancy of `datasetId`, `datasetPersistentId`, and `datasetType` fields for all dataset versions in the API documentation.

The first two have been around since v4.18, see also issue #6397

Author: poikilotherm

doc/sphinx-guides/source/api/native-api.rst

@@ -1583,6 +1583,9 @@ The fully expanded example above (without environment variables) looks like this
 
   curl "https://demo.dataverse.org/api/datasets/24/versions/1.0?excludeFiles=false"
 
+Note: the data object will contain the fields ``datasetId``, ``datasetPersistentId`` (since `4.18 <https://github.com/IQSS/dataverse/issues/6397>`_) and ``datasetType`` (since `6.7 <https://github.com/IQSS/dataverse/issues/11573>`_).
+All of these fields are equal and constant for all versions of a dataset.
+
 The optional ``excludeFiles`` parameter specifies whether the files should be listed in the output (defaults to ``true``). Note that a separate ``/files`` API can be used for listing the files, or a subset thereof in a given version. 
 
 .. code-block:: bash