Added migration guide (#37577)

* Migration guide added

Added migration guide from WindowsAzure.ServiceBus to Azure.Messaging.ServiceBus

* Update README.md

Added WindowsAzure.ServiceBus migration guide to README

* Update MigrationGuide-WindowsAzure-ServiceBus.md

Fixed typo

* Updated code snippets

* Update MigrationGuide-WindowsAzure-ServiceBus.md

* Apply suggestions from code review

Co-authored-by: Jesse Squire <[email protected]>

* Renamed migration guide for WindowsAzure.ServiceBus

* File rename

* Updated link to migration guide

* Update sdk/servicebus/Azure.Messaging.ServiceBus/MigrationGuide_WindowsAzureServiceBus.md

Co-authored-by: Madalyn Redding <[email protected]>

---------

Co-authored-by: Jesse Squire <[email protected]>
Co-authored-by: Madalyn Redding <[email protected]>