OBSERVATION_PERIOD filter as inclusion criteria need to include _start_date and _end_date

[pbr6cornell]

use case I ran into: I want to define primary criteria based on existance of various observations, and apply additional criteria (as includion rules in CALYPSO) based on how much observation period time exists before the cohort start date and observation period time after cohort start date. Ex: amongst patients with Disease X, how many have at least 6mo of observation prior? how many have at least 12mo of observation after cohort start date?