Write a function called to_grayscale that takes an RGB image (a numpy.array with shape (Height, Width, Color Channels)) and returns the same image but as a grayscale image (a numpy.array with shape (Height, Width)).

To transform an RGB image to grayscale image, we will use the luminosity formula for each pixel in the image Gray=0.21Red+0.72Green+0.07Blue. This is with python