Disposes the underlying transport if it is owned by the client, i.e. it was created via the Build method on HttpPipelineBuilder. If the underlying transport is not owned by the client, i.e. it was supplied as a custom transport on ClientOptions, it will not be disposed. The reason not to dispose a transport owned outside the client, i.e. one that was provided via ClientOptions is to account for scenarios where the custom transport may be shared across clients. In this case, it is possible to dispose of a transport still in use by other clients. When the transport is created internally, it can properly determine if a shared instance is in use.