By default, the prometheus exporter [appends timestamps to metrics](https://github.com/open-telemetry/opentelemetry-js/blob/b152497e5f77f35c5e49606da5b894bb8e5af00f/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts#L43). This goes against the current [guidance from OpenMetrics about whether to expose timestamps](https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#exposing-timestamps). We should consider not adding timestamps by default.