for use when we don't want API to serve any traffic, but paas is still
running. It's a simple nginx_buildpack app that is pushed separately,
and then two makefile commands that toggle the routes (and also
stop/start the nginx app).
For all endpoints/methods it returns a 503, with the response body.
```
{
"status_code": 503,
"errors": [
{
"error": "PlannedMaintenanceError",
"message": "We’re performing some essential updates. Notify will be back shortly. Please check https://status.notifications.service.gov.uk/ for more details"
}
]
}
```
NB: If you hit `/` it'll still return 404 - as this is defined in the
paas-proxy instance on aws.
