Clarified WizardView.get_form_prefix doc, refs #19024

    counter as string representing the current step of the wizard. (E.g., the

    first form is ``'0'`` and the second form is ``'1'``)

.. method:: WizardView.get_form_prefix(step, form)

.. method:: WizardView.get_form_prefix(step=None, form=None)

    Returns the prefix which will be used when calling the form for the given

    step. ``step`` contains the step name, ``form`` the form class which will

    be called with the returned prefix.

    If no ``step`` is given, it will be determined automatically. By default,

    this simply uses the step itself and the ``form`` parameter is not used.

    Given the step and the form class which will be called with the returned

    form prefix. By default, this simply uses the step itself.

    For more, see the :ref:`form prefix documentation <form-prefix>`.

.. method:: WizardView.get_form_initial(step)