Fix bug in Nds2ChannelType.find
This PR fixes a bug in Nds2ChannelType.find whereby valid NDS2 channel type strings (e.g. 'reduced') weren't being recognised because they didn't match the enum attribute name (e.g. 'RDS'). See https://git.ligo.org/nds/nds2-client/-/issues/118 for a short discussion of this naming choice in the NDS2 client.
This closes #1297 (closed) with the caveat that the correct NDS2 name for the channel is 'L1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01,reduced' (and not 'L1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01,rds').
Closes #1298.