Add 1D FFT examples

[tbirdso]

1D FFT filters were (relatively) recently ported from ITKUltrasound to ITK. Would be useful to have an example notebook demonstrating FFT plots (real, imaginary, modulus, phase) along one-dimensional scan lines. Meaningful example data can be taken from ITKUltrasound where one direction represents RF voltage waveform and other directions represent space or time dimensions.