docs: add warning about potential sensitive data in tracing (#12701)

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/OpenTelemetryTracingFactory.java

@@ -53,6 +53,18 @@ public class OpenTelemetryTracingFactory implements ApiTracerFactory {
   private final OpenTelemetry openTelemetry;
   private final ApiTracerContext apiTracerContext;
 
+  /**
+   * Warning: Traces may contain sensitive data such as resource names, full URLs, and error
+   * messages.
+   *
+   * <p>Before configuring subscribers or exporters for traces, review the contents of the spans and
+   * consult the <a href="https://opentelemetry.io/docs/security/handling-sensitive-data/">
+   * OpenTelemetry documentation</a> to set up filters and formatters to prevent leaking sensitive
+   * information, depending on your intended use case.
+   *
+   * <p>See also the <a href="https://opentelemetry.io/docs/concepts/semantic-conventions/">
+   * OpenTelemetry Semantic Conventions</a>.
+   */
   public OpenTelemetryTracingFactory(OpenTelemetry openTelemetry) {
     this(openTelemetry, null, ApiTracerContext.empty());
   }