feat(oohelperd): log messages at info level (#896)

We're using a request-specific logger where we also print the ID
of the request. This design helps to observe logs produced by
concurrent requests.

Part of https://github.com/ooni/probe/issues/2183

While there, fix https://github.com/ooni/probe/issues/2241

internal/cmd/oohelperd/logging.go

@@ -0,0 +1,41 @@
+package main
+
+import "github.com/ooni/probe-cli/v3/internal/model"
+
+// indexLogger is a logger with an index.
+type indexLogger struct {
+	indexstr string
+	logger   model.Logger
+}
+
+var _ model.Logger = &indexLogger{}
+
+// Debug implements DebugLogger.Debug
+func (p *indexLogger) Debug(msg string) {
+	p.logger.Debug(p.indexstr + msg)
+}
+
+// Debugf implements DebugLogger.Debugf
+func (p *indexLogger) Debugf(format string, v ...interface{}) {
+	p.logger.Debugf(p.indexstr+format, v...)
+}
+
+// Info implements InfoLogger.Info
+func (p *indexLogger) Info(msg string) {
+	p.logger.Info(p.indexstr + msg)
+}
+
+// Infov implements InfoLogger.Infov
+func (p *indexLogger) Infof(format string, v ...interface{}) {
+	p.logger.Infof(p.indexstr+format, v...)
+}
+
+// Warn implements Logger.Warn
+func (p *indexLogger) Warn(msg string) {
+	p.logger.Warn(p.indexstr + msg)
+}
+
+// Warnf implements Logger.Warnf
+func (p *indexLogger) Warnf(format string, v ...interface{}) {
+	p.logger.Warnf(p.indexstr+format, v...)
+}