Review the install scripts hosting

[tkapin]

Goals and Motivation

Recently, we've encountered .NET install scripts availability issues (reported as #487), which impacted all .NET customers that use the install scripts in their local development or continuous integration workflows. This outage has been observed and reported even by external customers on the internet. The root cause of the problem was unavailability of the https://dotnet.microsoft.com webpage, that is currently used to host the install scripts.

The goal of this issue is to review the current hosting of the install scripts, gather the requirements and design the hosting method that would ensure the following business objectives are met.

Business Objectives

• The install scripts are hosted reliably and the risk of issues like #487 repeating is minimized
• The release process of the install scripts is well defined and allows to deploy fixes quickly if needed
• Various other risks (e.g., throttling) are identified and accounted for in the design phase
• The hosting is designed so that it allows for changes in the future, if needed
• The hosting change is seamless from the customer perspective

There is already a suggestion of the solution described as #489, but this issue aims to ensure the change is designed and executed properly as any changes to the install script hosting methods present high risk to the wide range of customers.

[tkapin]

/FYI @baronfel, @JanKrivanek, @mmitche, @YuliiaKovalova

[YuliiaKovalova]

What about placing it next/close to the preview script in aka.ms/install-dotnet-preview that points to https://dotnetcli.blob.core.windows.net/dotnet/release/install-preview/install-dotnet-preview.sh blob storage ?

cc: @leecow