Add support for switching between 2011 and 2021 LSOA boundary definitions when geocoding/reverse-geocoding

2021 version of the LSOA boundaries is here: https://geoportal.statistics.gov.uk/datasets/ons::lower-layer-super-output-areas-december-2021-boundaries-ew-bsc-v4-2/about

Also need to add support for using the 2021 version of the Scottish "Data Zone" boundaries (equivalent of LSOA).