[exporters/prometheus] Omit underscore suffix for unitless metrics

[punya]

Fixes #2317

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #2323 (d23b902) into main (ca67af0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2323   +/-   ##
=======================================
  Coverage   87.45%   87.45%           
=======================================
  Files         199      199           
  Lines        5997     5997           
=======================================
  Hits         5244     5244           
  Misses        753      753           

[marcalff]

@punya

Our CI uses clang-format 10

To fix the format error, either run clang-format, or take the diff from the ci format logs and apply it manually:

diff --git a/exporters/prometheus/src/exporter_utils.cc b/exporters/prometheus/src/exporter_utils.cc
index 95ff12a..e115500 100644
--- a/exporters/prometheus/src/exporter_utils.cc
+++ b/exporters/prometheus/src/exporter_utils.cc
@@ -43,7 +43,8 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
       auto sanitized   = SanitizeNames(origin_name);
       prometheus_client::MetricFamily metric_family;
       metric_family.name = sanitized;
-      if (!unit.empty()) {
+      if (!unit.empty())
+      {
         metric_family.name += "_" + unit;
       };
       metric_family.help = metric_data.instrument_descriptor.description_;
diff --git a/exporters/prometheus/test/exporter_utils_test.cc b/exporters/prometheus/test/exporter_utils_test.cc
index 8de1721..679c291 100644
--- a/exporters/prometheus/test/exporter_utils_test.cc
+++ b/exporters/prometheus/test/exporter_utils_test.cc
@@ -162,7 +162,7 @@ TEST(PrometheusExporterUtils, HandleMissingUnit)
   TestDataPoints dp;
   metric_sdk::ResourceMetrics data = dp.CreateSumPointData("");
   std::vector<prometheus::MetricFamily> family =
-    PrometheusExporterUtils::TranslateToPrometheus(data);
+      PrometheusExporterUtils::TranslateToPrometheus(data);
   ASSERT_EQ(family.begin()->name, "library_name");
 }

[punya]

Abandoning because this problem is already solved in #2213 as part of a larger change.