SB Track2- Migration guide

[hemanttanwar]

Create Migration guide

[ramya-rao-a]

We have a version of the guide in a feature branch: https://github.com/conniey/azure-sdk-for-java/blob/feature/session-receiver/sdk/servicebus/azure-messaging-servicebus/migration-guide.md

Moving this issue to the next milestone for cherry-picking to master