Clarify Prometheus translation ownership

Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverter.java

@@ -574,10 +574,12 @@ private static String convertLegacyLabelName(String key) {
       throw new IllegalArgumentException("label name is empty");
     }
 
-    // The OTel compatibility spec requires invalid attribute-name characters and repeated
-    // underscores to collapse to a single "_". Prometheus label names beginning with "__" are
-    // reserved for internal labels like "__name__" and scrape/relabel labels, and Prometheus Java
-    // rejects them as user labels, so do not preserve "__...__" reserved-looking names here.
+    // OTel owns OTLP-to-Prometheus translation. Prometheus Java validates and serializes names,
+    // but no longer owns this naming mangling. The OTel compatibility spec requires invalid
+    // attribute-name characters and repeated underscores to collapse to a single "_". Prometheus
+    // label names beginning with "__" are reserved for internal labels like "__name__" and
+    // scrape/relabel labels, and Prometheus Java rejects them as user labels, so do not preserve
+    // "__...__" reserved-looking names here.
     StringBuilder result = new StringBuilder(key.length());
     boolean previousWasUnderscore = false;
     for (int i = 0; i < key.length(); ) {