Enhanced the `authentication/:id/import_users` interface for a more user-friendly user import feature:
-- Add new parameter `?type=plain` to support importing users with plaintext passwords in extension to the current solution which only supports password hash.
+- Add new parameter `?type=plain` to support importing users with plaintext passwords in addition to the current solution which only supports password hash.
- Support `content-type: application/json` to accept HTTP Body in JSON format in extension to the current solution which only supports `multipart/form-data` for csv format.