Improve Logging / Error reporting - bad local config is producing HTTP 503 DataServiceUnavailable

On my local machine, trying to get a list of project transfers via http://localhost:8000/api/v2/duke-ds-project-transfers/, the DRF browser shows the following error:

```
HTTP 503 Service Unavailable
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
"detail": "'NoneType' object has no attribute 'client_id'"
}
```

It appears to be catching an exception due to GCB-web-auth misconfiguration, but reporting it as DataServiceUnavailable.