Use coord tracing code in the trace example to return the loop intensities

[nabobalis]

In that case, we should expand the tracing example to:

"I think we should just use the coord tracing stuff we have in sunpy to show how once you have the SkyCoord you can extract the intensities a la https://docs.sunpy.org/en/stable/generated/gallery/units_and_coordinates/map_slit_extraction.html#sphx-glr-generated-gallery-units-and-coordinates-map-slit-extraction-py"