Submit a BLPAPI request

Submits a request to a Bloomberg Open API service. The namespace, service, and request type are specified via query parameters, and the request payload is sent as JSON in the body. Currently supports the //blp/refdata service (for ReferenceDataRequest, HistoricalDataRequest, IntradayBarRequest, and IntradayTickRequest) and the //blp/apiflds service (for FieldInfoRequest and FieldSearchRequest).