(Azure CXP)Tech Doc Update

Added credentials.azure.com on line 78 as this is also one URL without allowing which, the MFA extension setup fails. 

Verified this internally and found that Credentials.azure.com is MFACAPPP (Credential Authentication Provider and Proxy) Service . It can be checked in Internal AAD PG teams wiki . 

This is as per  MicrosoftDocs/azure-docs#42684

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cc: @iainfoulds

Author: shashishailaj

articles/active-directory/authentication/howto-mfa-nps-extension.md

@@ -75,6 +75,7 @@ The NPS server needs to be able to communicate with the following URLs over port
 
 - https:\//adnotifications.windowsazure.com
 - https:\//login.microsoftonline.com
+- https:\//credentials.azure.com
 
 Additionally, connectivity to the following URLs is required to complete the [setup of the adapter using the provided PowerShell script](#run-the-powershell-script)