refactor: move scrubbingLogger to the scrubber pkg (#394)

* refactor: move scrubbingLogger to the scrubber pkg

We need it exported so we can use it in the new implementation.

Part of https://github.com/ooni/probe/issues/1687

* fix test

internal/scrubber/logger.go

@@ -0,0 +1,62 @@
+package scrubber
+
+import "fmt"
+
+// UnderlyingLogger defines the common interface that a logger should have. It is
+// out of the box compatible with `log.Log` in `apex/log`.
+type UnderlyingLogger interface {
+	// Debug emits a debug message.
+	Debug(msg string)
+
+	// Debugf formats and emits a debug message.
+	Debugf(format string, v ...interface{})
+
+	// Info emits an informational message.
+	Info(msg string)
+
+	// Infof formats and emits an informational message.
+	Infof(format string, v ...interface{})
+
+	// Warn emits a warning message.
+	Warn(msg string)
+
+	// Warnf formats and emits a warning message.
+	Warnf(format string, v ...interface{})
+}
+
+// Logger is a Logger with scrubbing. All messages are scrubbed
+// including the ones that won't be emitted. As such, this logger
+// is less efficient than a logger without scrubbing.
+type Logger struct {
+	UnderlyingLogger
+}
+
+// Debug scrubs and emits a debug message.
+func (sl *Logger) Debug(message string) {
+	sl.UnderlyingLogger.Debug(Scrub(message))
+}
+
+// Debugf scrubs, formats, and emits a debug message.
+func (sl *Logger) Debugf(format string, v ...interface{}) {
+	sl.Debug(fmt.Sprintf(format, v...))
+}
+
+// Info scrubs and emits an informational message.
+func (sl *Logger) Info(message string) {
+	sl.UnderlyingLogger.Info(Scrub(message))
+}
+
+// Infof scrubs, formats, and emits an informational message.
+func (sl *Logger) Infof(format string, v ...interface{}) {
+	sl.Info(fmt.Sprintf(format, v...))
+}
+
+// Warn scrubs and emits a warning message.
+func (sl *Logger) Warn(message string) {
+	sl.UnderlyingLogger.Warn(Scrub(message))
+}
+
+// Warnf scrubs, formats, and emits a warning message.
+func (sl *Logger) Warnf(format string, v ...interface{}) {
+	sl.Warn(fmt.Sprintf(format, v...))
+}