[Event Hubs] Loosen fully qualified namespace validation

[jsquire]

Summary

Currently, developers are required to pass in a fully qualified namespace name with the assumption that it is formatted as a host name. The intention is that the value would be obtained from the Azure portal, where a Host name field exists as metadata for the resource. However, this restriction causes a poor experience when using the management library, CLI, Bicep, or ARM template to create the namespace, as the resource provider does not return a host name. The resource provider returns only an endpoint attribute the namespace, formatted as "https://my-namespace.servicebus.windows.net". With the current validation, developers must parse the endpoint into the correct format for client use, causing friction.

Scope of work

• Update client construction to accept a URI format as valid for the fully qualified namespace name

Success Criteria

• Construction for all client types accept a fully qualified namespace in URI format.
• When a URI is passed for client construction, it is parsed to extract the host name.
• If the host name does not pass existing fully qualified namespace validation, it is rejected.
• Any existing tests for rejecting URI-formatted fully qualified namespace values have been adjusted.
• New tests necessary to validate the feature have been created and pass reliably.
• The existing test suite continues to produce deterministic results and pass reliably.

[jsquire]

//cc: @conniey, @anuchandy, @lmolkova