Add geometry for Null Island buoy and Null Island exclusion zone

[almccon]

According to this drawing from NOAA, the diameter of the Null Island buoy is 2.3m.

Also, there is apparently a five nautical mile exclusion zone around the buoy, although the only citation I can find for this doesn't seem to be an official source. It seems likely that this means a 5nm radius not _diameter, but I'd like to get confirmation of that.

It would be nice to add these geometries too.