Update chng-county geomapping to use CHNG syntax

[krivard]

CHNG county groupings are reported in the raw files using underscore-delimited FIPS instead of a unique identifier for each group:

[indicators@delphi-master-prod-01 changehc]$ zgrep _ cache/20230723_Counts_Products_Mixed.dat.gz |head
19491222,06049_06035,3 or less
20020120,08053_08111_08091_08033_08113_08085,3 or less
20091014,06049_06035,3 or less
20151023,32017_32003,3 or less
20151123,32017_32003,3 or less
20151223,32017_32003,3 or less
20160123,32017_32003,3 or less
20160223,32017_32003,3 or less
20160323,32017_32003,3 or less
20160423,32017_32003,3 or less

#1858 let us continue acquiring CHNG data by temporarily dropping chng county groupings from the pipeline, but we should update the geo parsing and mapping code to accept this underscore format.