ENH: Add default radius value to NewFunctorFilter overload
This should allow the usage described at the bottom of https://www.orfeo-toolbox.org/CookBook-8.0/C++/FunctorImageFilter.html#number-of-output-bands.
This should allow the usage described at the bottom of https://www.orfeo-toolbox.org/CookBook-8.0/C++/FunctorImageFilter.html#number-of-output-bands.