message: Fix mislabeled Doxygen parameter names
  This fixes a -Wdocumentation warning for clang-10.
diff: @@ -407,8 +407,8 @@ public:
  /// as well as prefixes starting with an underscore are
  /// reserved.
  /// @param name The human-readable name of the metric, e.g., `requests`.
  - /// @param label_names Names for all label dimensions of the metric.
  - /// @param default_upper_bounds Upper bounds for the metric buckets.
  + /// @param labels Names for all label dimensions of the metric.
  + /// @param upper_bounds Upper bounds for the metric buckets.
  /// @param helptext Short explanation of the metric.
  /// @param unit Unit of measurement. Please use base units such as `bytes` or
  /// `seconds` (prefer lowercase). The pseudo-unit `1` identifies
  