Fix feature_flag.evaluations metric count always being zero

The OTel SDK defaults to DELTA temporality for counters. The Datadog
agent converts OTLP delta monotonic sums to rate metrics by dividing
by the export interval (10s). Five evaluations in under 1s produce
~0.5, which rounds to zero in the points payload.

Force CUMULATIVE temporality on the OtlpHttpMetricExporter so the
agent receives an absolute count rather than a rate, making
test_ffe_eval_metric_count reliable.

Author: typotter

products/feature-flagging/feature-flagging-api/src/main/java/datadog/trace/api/openfeature/FlagEvalMetrics.java

@@ -9,6 +9,7 @@
 import io.opentelemetry.api.metrics.Meter;
 import io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporter;
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.export.AggregationTemporalitySelector;
 import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
 import java.io.Closeable;
 import java.time.Duration;
@@ -59,7 +60,10 @@ class FlagEvalMetrics implements Closeable {
       }
 
       OtlpHttpMetricExporter exporter =
-          OtlpHttpMetricExporter.builder().setEndpoint(endpoint).build();
+          OtlpHttpMetricExporter.builder()
+              .setEndpoint(endpoint)
+              .setAggregationTemporalitySelector(AggregationTemporalitySelector.alwaysCumulative())
+              .build();
 
       PeriodicMetricReader reader =
           PeriodicMetricReader.builder(exporter).setInterval(EXPORT_INTERVAL).build();