log: Store http request/responses in a log file (#4804)

When MINIO_TRACE_DIR is provided, create a new log file and store all
HTTP requests + responses data, body are excluded to reduce memory
consumption. MINIO_HTTP_TRACE=1 enables logging. Use non mem
consuming http req/resp recorders, the maximum is about 32k per request.
This logs to STDOUT, body logging is disabled for PutObject PutObjectPart
GetObject.

cmd/globals.go

@@ -125,6 +125,9 @@ var (
 	globalHTTPServerErrorCh = make(chan error)
 	globalOSSignalCh        = make(chan os.Signal, 1)
 
+	// Enable HTTP request/response headers and body logging.
+	globalHTTPTrace bool
+
 	// List of admin peers.
 	globalAdminPeers = adminPeers{}