[azservicebus] Snippets and examples cleanup

[richardpark-msft]

We've changed how we want to present snippets and examples. We can take advantage of this in azservicebus.

1. Convert any snippets in the readme to Example_Test files. It makes sense that these would end up as whole-file examples instead.
2. Change the credentials authentication to be similar to what I've done in the azeventhubs readme. A bullet point list, pointing to the individual examples in pkg.go.dev.
3. Make sure the examples don't have references to non-standard functions (ie: exitOnError)

[github-actions]

Hi @richardpark-msft, we deeply appreciate your input into this project. Regrettably, this issue has remained unresolved for over 2 years and inactive for 30 days, leading us to the decision to close it. We've implemented this policy to maintain the relevance of our issue queue and facilitate easier navigation for new contributors. If you still believe this topic requires attention, please feel free to create a new issue, referencing this one. Thank you for your understanding and ongoing support.