Save http trace to a file (#5300)

Save http trace to a file instead of displaying it onto the console.
the environment variable MINIO_HTTP_TRACE will be a filepath instead
of a boolean.

This to handle the scenario where both json and http tracing are
turned on. In that case, both http trace and json output are displayed
on the screen making the json not parsable. Loging this trace onto
a file helps us avoid that scenario.

Fixes #5263

cmd/globals.go

@@ -123,8 +123,8 @@ var (
 	globalHTTPServerErrorCh = make(chan error)
 	globalOSSignalCh        = make(chan os.Signal, 1)
 
-	// Enable HTTP request/response headers and body logging.
-	globalHTTPTrace bool
+	// File to log HTTP request/response headers and body.
+	globalHTTPTraceFile *os.File
 
 	// List of admin peers.
 	globalAdminPeers = adminPeers{}