Added new example for getting colormaps #2865
So I rebased and decided that we also do not need the reference colormap example. I added it to the new example.
Since the CI is on fire, the only build we care about is the docs one.
Looks good to me.
Can we set the second image (the one with all the colourmaps) as the thumbnail? i.e. https://sphinx-gallery.readthedocs.io/en/latest/auto_examples/plot_choose_thumbnail.html