Empty Landing Page

## Problem
When you use an Azure Function app as a backend pool for Azure Front Door, it quickly generates large bandwidth charges over the course of a few days.

This is even true if the function app is itself functionless.

## Cause
The bandwidth charges are a result of the health probe checks Azure Front Door makes to any of its backend pools.

For an Azure Function app, this would be the landing page, which is around 146 KBs. Since the probes are continuous and can be many over the course of a minute (due to Azure Front Door's many edges around the world), this quickly passes the free monthly outbound Data provision of 5GB in just a few hours and starts accumulating costs.

## Solution
Provide customer with the option to use an empty landing page (blank html) that results in a few bytes per health probe check.

The disable landing page option currently returns a 204 status code that results in health probe failures. Azure Front Door only accepts a 200 status code.

Start by locating the existing disable landing page option and the handling that currently returns a 204 response. Check how the Azure Functions host serves the landing page and how Azure Front Door health probes interact with it. Done means an optional empty HTML response returns HTTP 200 with only a few bytes, while preserving the current behavior for users who do not choose it.

Written by the indexing model from the issue text.