Automate the creation of Azure app registration

[devkeydet]

In order for the code running in azure to work, we need to register an Azure AD app:

https://docs.microsoft.com/en-us/azure/active-directory/develop/active-directory-integrating-applications

Currently it is a prerequisite to do this before using the release example. It should be part of the release automation. There is a good blog post showing how to do this here:
http://blog.octavie.nl/index.php/2017/09/13/creating-azure-ad-app-registration-with-powershell-part-1
http://blog.octavie.nl/index.php/2017/09/19/create-azure-ad-app-registration-with-powershell-part-2

Specifically, the release should have a PowerShell script that does the following:

• Check for the existence of the app registration by name (passed as a parameter to the script)
• If it exists, verify it has the right permissions
• If it doesn't exist, create it and set the right permissions

The permission that need to be set are in the attached screenshot.

Once the application is created, we need to get the values needed for subsequent tasks and put them into the existing VSTS variables.