We rewrote the distribution portion of the parser to better reflect the n:1
relationship between GSP groups and distributors. The .gsp_group_id
(str) is gone, replaced with .gsp_groups (list[str]).
The API for DNOs and IDNOs are now the same, dropping properties like
.licensee and mpas_operator_id in favour of a common participant_id.
See the docs for specifics.