Document Beyla integration with OTEL collectors and prometheus scrapers

[mariomac]

• When Beyla exports OTEL data to an OTEL collector or Alloy, we should document that honor_labels is required to avoid the collector overriding the instance ID as provided by Beyla. Beyla provides an instance ID per monitored process, but the collector would override it by a common Beyla instance ID.

• Check if something is needed when exporting the data via Prometheus, such as making sure that instance is the service_instance_id field.