Add Exemplars support for the OpenTelemetry Exporter

[fstab]

Exemplars are not implemented yet in the OpenTelemetry exporter. We should add support for that.

https://github.com/prometheus/client_java/blob/586c2f9e4c62553eb157c82b292377521375f554/prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/otelmodel/PrometheusData.java#L47C48-L47C48