Method to add domains to the suppression list.
https://api.wbsrvc.com/SuppressionList/ImportDomains/
POST
| user_key Required |
User Key of the user who initiates the call. Type: string |
| domain Required |
List of domains. Type: array of domains - i.e. array('test.com') |
| client_id Optional |
ID of the client. Type: integer |