Same as calling 'sendRequest(requestTemplate, null)'

Send a request defined by the specified 'requestTemplate'. If the optionally specified 'correlationId' is supplied, use it otherwise create a new 'CorrelationId'. The actual 'CorrelationId' used is returned. A successful request will generate zero or more 'PARTIAL_RESPONSE' events followed by exactly one 'RESPONSE' event. Once the final 'RESPONSE' event has been received the 'CorrelationId' associated with this request may be re-used. If the request fails at any stage a 'REQUEST_STATUS' will be generated after which the 'CorrelationId' associated with the request may be re-used.