Missing converter for astropy.coordinates.representation.geodetic

[braingram]

There does not appear to be a converter for the following

WGS84GeodeticRepresentation
WGS72GeodeticRepresentation
GRS80GeodeticRepresentation

Now found in astropy.coordinates.representation.geodetic
https://github.com/astropy/astropy/blob/9ec5277724150ea178282f5dfbd9ca8782f89021/astropy/coordinates/representation/geodetic.py#L103-L121

This causes the current test suite to fail as discussed in this PR:
#181

[braingram]

Running the following with:

• asdf-astropy 0.4.0
• astropy 5.2.2

import asdf
import astropy.units as u
import astropy.coordinates.earth

r = astropy.coordinates.earth.WGS84GeodeticRepresentation(lat=0 * u.rad, lon=0 * u.rad, height=0 * u.m)
asdf.AsdfFile({'r': r}).write_to('foo.asdf')

fails with

yaml.representer.RepresenterError: ('cannot represent an object', <WGS84GeodeticRepresentation (lon, lat, height) in (rad, rad, m)
    (0., 0., 0.)>)