Create and register OTel entities from pipelines built by the controller

[lquerel]

In the document docs/telemetry/entity-model.md, we defined the entity modeling that we want to associate with the metrics and events produced by the OTAP Dataflow Engine.

Today, in the internal telemetry system (crates/telemetry), we support the concepts of AttributeSet, MetricSet, and MetricsRegistry. As currently defined, all attribute sets are entity-based attributes. To enable reuse of these entity attributes, we need to extract them into a dedicated EntityRegistry, and we also need to update the metrics registry to reference these entities.

Once this is in place, the internal event reporting system will also be able to reference the same entity attributes.