A simplified Flink SQL Gateway. Will be replaced by the real GW once upgraded for Flink 1.13 API is implemented according to https://docs.google.com/document/d/1DKpFdov1o_ObvrCmU-5xi-VrT6nR2gxq-BbswSSI9j8/edit#heading=h.cje99dt78an2
REST call implemented will be POST/v1/sessions/:session_id/statements
in case of success status line will be 200 "OK"
Return body will be {"id": id} containing the flink id