Add examples on how to create non-equal spaced WCS

[hayesla]

Describe the feature

Its hard to construct a WCS that's not FITS-WCS, say with non-equally spaced values etc

Proposed solution

We should new examples of how to do this, and a helper functions for doing this

[hayesla]

from the discussion at coordination meeting from @Cadair

from sunpy.net import Fido, attrs as a
import sunpy.map
from ndcube.wcs.wrappers import CompoundLowLevelWCS
from ndcube import NDCube
from ndcube.extra_coords import QuantityTableCoordinate
import astropy.units as u
import matplotlib.pyplot as plt

aia_files = Fido.fetch(Fido.search(a.Time("2023/01/01", "2023/01/01 00:00:11"), a.Instrument.aia))
maps = sunpy.map.Map(aia_files, sequence=True)
# Sort the map sequence in place
maps.maps = list(sorted(maps.maps, key=lambda m: m.wavelength))
waves = u.Quantity([m.wavelength for m in maps])
wave_wcs = QuantityTableCoordinate(waves, physical_types="em.wl", names="wavelength").wcs
cube_wcs = CompoundLowLevelWCS(wave_wcs, maps[0].wcs)
mycube = NDCube(maps.as_array(), wcs=cube_wcs)
mycube.plot(plot_axes=['y', 'x', None])
plt.show()