Add support for Unknown value grouping
- Add new value to GROUP_MAPPING Enum
- In the SPARQL results of get_grouping_information and _get_grouping_counts_from_sparql, recognize the 'unknown value' URLs as such and consolidate all of the lines into one dictionary entry
- Update all unit tests added in previous commits
- Re-sort the OrderedDict in retrieve_and_process_data, to avoid the unknown_value grouping being out of order
- Add to the queries endpoint some more dancing to recognize this new special grouping − this could use some refactoring.
Bug: T273226