Attribute Macro subclient Copy item path

Attribute client subclient struct declarations to enable distributed tracing.

To declare a subclient that will be traced, you should use the #[tracing::subclient] attribute exported from azure_core.

This macro will automatically instrument the subclient declaration with tracing information. It will also ensure that the subclient is created with the necessary tracing context. The #[tracing::subclient] attribute takes a single argument, which is a string representing the Azure Namespace name for the service being traced.