refactor: add @filterable tag to filterable properties

src/things/message.ts

@@ -36,11 +36,15 @@ export interface SCMessageWithoutReferences
 
   /**
    * Roles for which the message is intended
+   *
+   * @filterable
    */
   audiences: SCMessageAudience[];
 
   /**
    * When the message was created
+   *
+   * @filterable
    */
   dateCreated?: SCISO8601Date;