Add changelog for 6832

Author: jenshnielsen

docs/changes/newsfragments/6832.improved

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+``DelegateParameter`` now includes validators of its source Parameter into its validators. This ensures that a ``DelegateParameter``
+with a non numeric source parameter is registered correctly in a measurement when the ``DelegateParameter`` it self does not
+set a validator. Furthermore `DelegateParameter`` has gained a ``root_source`` attribute that makes it easier to get the
+root source of a ``DelegateParameter`` that delegates to another ``DelegateParameter``.