Annotate any class that needs to be a long-lived service within the node, such as an oracle, with this annotation.
Such a class needs to have a constructor with a single parameter of type
interface ServiceHub. This constructor will be invoked
during node start to initialise the service. The service hub provided can be used to get information about the node
that may be necessary for the service. Corda services are created as singletons within the node and are available
to flows via ServiceHub.cordaService.