implementation of extension methods to configure databus

Implementation of Fluent API (`ConfigureAzureDataBus`) to provide code-based configuration alternative to config section (`AzureDataBusConfig`).
Both utilize `AzureDataBusGuard` to perform validation.

Please review @yvesgoeleven @johnsimons @SimonCropp 
Should the check be `string.IsNullOrWhiteSpace`