Request: load existing cohort of patients

[am202]

We've had cases where users will already have a cohort of patients, and they want to view datasets for those patients. It would be helpful if there was a way to load that cohort into Leaf.

I could imagine different ways of implementing that. It could be a generalized mechanism for searching for possible string values of a variable concept, which might require adding an IsText column to the concept table (similar to IsNumeric, which would let the UI know to allow the user to enter string values to query) and also SqlFieldText (similar to SqlFieldNumeric, which Leaf could use when building the query, adding something like "where [value of SqlFieldText] in ( [list of values user entered into UI] )" to the query.

Or it could be a mechanism specific to this use case, maybe something that allows a user to enter values to search for in the MRN column from the basic demographics dataset. It could also allow a user to supply a file containing the values to query.