Add Drug Benefit Flag to Payer Plan Table

@Gowtham_Rao, thanks for the confirmation. And, I love the idea of payer_ids representing payers. I believe we talked about this a year ago (the original poster being @aguynamedryan here) and I still stand by the recommendation. We now have to create concept_ids for payers using the payer ids. We may have to add a field to the payer_plan_period table.