Era fy cohort

[gowthamrao]

We sometimes use SQL to generate cohorts that conform to the structure that is cohort_definition_id, subject_id, cohort_start_date, cohort_end_date

But - these sql may not conform as described here OHDSI/CohortGenerator#36

If not conforming, then we can make it conforming using the cohort era logic in Circe https://github.com/OHDSI/circe-be/blob/4504aa27efa6bd16ab247b969e740fb005daa6a8/src/main/resources/resources/cohortdefinition/sql/generateCohort.sql#L65-L114

It would nice if cohort generator is able to just executed this SQL, delete and insert the person level data back into the cohort table - after era fying using the circe code.