Team admin can add billing contacts

How it was found

Billing contacts can only be added by team owners. However, team admin can escalate his privileges and add billing contacts.

Steps to reproduce: 1.Log in as team admin 2.Send the below request using his token and it adds '[email protected]' to billing contacts.

POST /api/team.billing.addContact HTTP/1.1 Host: satishb3mailinator.slack.com Content-Type: application/x-www-form-urlencoded; charset=UTF-8 Content-Length: 106

email=[email protected]&token=xoxs-3206092076-3204538285-3743137121-836b042620&set_active=true&_attempts=1

To confirm, login as team owner and navigate to billing contacts. Notice that [email protected] is added to billing contact list.