Update split SDK to 6.0.2 to fix sync bug (#17060)

* Update split SDK to 6.0.2 to fix sync bug

* Vendor and tidy

vendor/github.com/splitio/go-toolkit/v4/logging/interface.go

@@ -0,0 +1,12 @@
+package logging
+
+// LoggerInterface ...
+// If a custom logger object is to be used, it should comply with the following
+// interface. (Standard go-lang library log.Logger.Println method signature)
+type LoggerInterface interface {
+	Error(msg ...interface{})
+	Warning(msg ...interface{})
+	Info(msg ...interface{})
+	Debug(msg ...interface{})
+	Verbose(msg ...interface{})
+}