Edit Members API annotation

grape-swagger only selects the first option in types because OpenAPI V2 does not support multiple types. As such, the generated documentation will not show that user_id is actually a comma-separated array. This bridges the discrepancy between OpenAPI and Rails annotations by using Validations::Types::CommaSeparatedToIntegerArray.coerce to support the comma-separated array.

This also fixes the success object as grape-swagger could not find ::Entities::Member, causing generation to fail.

The OpenAPI V2 documentation will be used for dogfooding API fuzzing as per #372422 (closed) and the OpenAPI autogeneration &8926.