Add IFO-specific 20-bit DAC suspension channels
Recently it was realized that the 4x output reduction on ETMX L3 channels that we perform for LHO does not apply for LLO, and that LLO has its own 20-bit channels that need reduction (ETMY L3 channels). Site-specific 20-bit channels have been designated, as well as dates when those 20-bit DAC switches were implemented.
LLO accidentally-increased ETMY saturation: https://ldas-jobs.ligo-la.caltech.edu/~lockloss/events/1259/568498/saturations_ZOOM.png
LLO corrected ETMY saturation: https://ldas-jobs.ligo-la.caltech.edu/~yannick.lecoeuche/events/1259/568498/saturations_ZOOM.png
LLO accidentally-reduced ETMX saturation: https://ldas-jobs.ligo-la.caltech.edu/~lockloss/events/1259/435400/saturations_WIDE.png
LLO corrected ETMX saturation: https://ldas-jobs.ligo-la.caltech.edu/~yannick.lecoeuche/events/1259/435400/saturations_WIDE.png
Closes #136 (closed)