Provide a way to register custom modules with the Geojson ObjectMapper.

[amanbhurji]

Currently if a user wants to do some object serialization using some custom modules, they will be required to override the GeoJson classes and use their own mapper. That could be avoided if it were possible to register custom modules with the Mapper here

[bjornharrtell]

@amanbhurji are you still interested in getting this in?

[boundaries-io]

Would it be possible to have this implemented.