Add release note

releasenotes/notes/feat-tensor-class-2ad38ba7246ccbd5.yaml

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+---
+features:
+  - |
+    Adds the new :class:`~qiskit_nature.second_q.operators.Tensor` class used
+    internally to consistently deal with n-dimensional tensors throughout the
+    stack.
+  - |
+    Adds the new :attr:`~qiskit_nature.settings.tensor_wrapping` setting which
+    may be set to ``True`` to enable automatic wrapping of any n-dimensional
+    tensor stored inside a
+    :class:`~qiskit_nature.second_q.operators.PolynomialTensor` into a
+    :class:`~qiskit_nature.second_q.operators.Tensor` instance.
+deprecations:
+  - |
+    Deprecated the default value (``False``) of
+    :attr:`~qiskit_nature.settings.tensor_wrapping` meaning that in the future
+    :meth:`~qiskit_nature.second_q.operators.PolynomialTensor.__getitem__` will
+    return objects of type :class:`~qiskit_nature.second_q.operators.Tensor`.