Add support for URL Authorization Rules in Azure Functions

When adding Authentication/Authorization to an Azure Function App, all functions in the App are by default protected.

I am experiencing the exact issue as described in this article when using Traffic Manager:

https://blogs.msdn.microsoft.com/jpsanders/2017/02/06/azure-traffic-manager-probe-degraded-due-to-401-from-azure-web-app/

A similar feature was added to Azure Web Apps and it would be nice to see this feature added to Azure Functions to allow Traffic Manager to ping a Function that allows anonymous requests.

The workaround today is to allow anonymous requests for the entire Function App

#### Repro steps

1) Create an Azure Function App with Authentication/Authorization enabled.
2) Add a Function.
3) Create a Traffic Manager resource that points the Function App.

#### Actual behavior

The Endpoint is always reported as degraded because either the app returns 401 or 30x for redirect to the auth server.

#### Known workarounds

Allow anonymous requests in the Authentication configuration.

Start with the listed repro steps in the issue and review the linked Azure Traffic Manager article to understand the 401/30x probe failure. Trace the Azure Functions Authentication/Authorization configuration involved in protecting all functions. Done means a URL authorization rule can allow the Traffic Manager probe while preserving authentication for other functions.

Written by the indexing model from the issue text.