Add change log

Author: getgaurav2

doc/whats_new/upcoming_changes/sklearn.model_selection/16236.feature.rst

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+Added group-aware functionality to :class:`~sklearn.model_selection.TimeSeriesSplit`.
+The ``groups`` parameter now allows for proper cross-validation of time series data 
+with multiple groups, ensuring temporal order is preserved within each group while 
+maintaining the time-based splitting behavior.
+By :user:`Gaurav Chwla <getgaurav2>`