Missing billing account causes the legacy challenge activation to fail

[ThomasKranitsas]

When activating a legacy challenge the legacy processor throws 500 error because of missing billing account (Billing/PO Number is null/empty.)

As a temporary solution, the V5 Challenge API will call the https://api.topcoder.com/v3/direct/projects/<directProjectId> endpoint to fetch the billing account for the given project ID.

If the billing account does not exist, it'll not let you set the status to Active as the activation won't be possible on the legacy system.

Implications:

1. We can’t create an Active challenge. We need to create it as Draft and then update it so the legacy processor populates the directProjectId
2. We can’t update to Active unless the processor has created the challenge on legacy first
3. if either the billing account or the directProjectId is missing, The API will throw a 400 error

cc @rootelement