message: Add back in opt of for namespacing.
diff: @@ -192,6 +192,13 @@ std::string PrometheusStatsFormatter::formattedTags(const std::vector<Stats::Tag
  }
  std::string PrometheusStatsFormatter::metricName(const std::string& extracted_name) {
  + // Offer a way to opt out of automatic namespacing.
  + // If metric name starts with "_" it will be trimmed but not namespaced.
  + // It is the responsibility of the metric creator to ensure proper namespacing.
  + if (extracted_name.size() > 1 && extracted_name[0] == '_') {
  + return sanitizeName(extracted_name.substr(1));
  + }
  +
  std::string sanitized_name = sanitizeName(extracted_name);
  absl::string_view prom_namespace{sanitized_name};
  