UI needs an API explaining why a function isn't indexed or is returning 404

Currently the UI queries a function's keys. If that fails for any reason, we query the function status, if that also fails, we query the host status.
However we still have cases where keys is 404, status is 404, and host status is 200 no errors. More logs and analysis are included in an email with subject `[Azure/Azure-Functions] Getting error: "We are not able to retrieve the keys for function "`

Of course part of the problem stems from having 2 parts interpreting what a function is (kudu and the runtime)