Notebooks that still need modernising

[HarriKeenan]

The following notebooks need updating before they can work.

• aux_coord_factory.ipynb - this creates a custom aux factory subclass but aux factories have changed a lot since it was written so the code needs major revisions to correctly subclass the modern version of aux factory
• ocean_buoy_regridding.ipynb - uses some complex index assignment that no longer works, it now gets a broadcasting error, needs some detailed debugging
• plotting_wmts_with_cartopy.ipynb - the webmap tile service URL needs updating and then the appropriate map tiles need to be found within the new service, new URL : https://gibs.earthdata.nasa.gov/wmts/epsg4326/best/wmts.cgi