feat: created_via for tracking how runners got into the system (#212)

close #211

squash merge please:)

Reviewed-on: #212

src/models/actions/create/CreateSelfServiceRunner.ts

@@ -28,6 +28,7 @@ export class CreateSelfServiceRunner extends CreateParticipant {
     public async toEntity(group: RunnerGroup): Promise<Runner> {
         let newRunner: Runner = new Runner();
 
+        newRunner.created_via = "selfservice";
         newRunner.firstname = this.firstname;
         newRunner.middlename = this.middlename;
         newRunner.lastname = this.lastname;