different behavior addCdmName and addCohortName

[catalamarti]

If the column already exists:

• addCdmName overwrites it
• addCohortName two resultant columns are created: cohort_name.x and cohort_name.y

what behavior do we want?

[xihang-chen]

I think overwrite for addCohortName() makes more sense. Although I think it could be nice to throw an warning that it has been overwritten.

A user that uses these functions probably don't know these columns already exist in their data frame so I think overwrite is fine. Plus I don't think cohort_name.x and cohort_name.y are informative column names.

[catalamarti]

agreed
-> change addCohortName to overwrite column if this already exist (throw warning/message)