refactor(otel): centralize tag keys, align with semconv, and unify ITraceable

[falberthen]

Refactored

• Add TelemetryTags + MessagingAttributes constants under Core.Infrastructure/OpenTelemetry.
• Migrate Kafka and outbox spans to the current OTel messaging semconv attribute names.
• Carry OrderId in ProcessPayment/ProcessShipment so they implement ITraceable.
• Switch ITraceable value type to object; CommandBus is now the single point of span enrichment.
• Update tests for new ProcessPayment/ProcessShipment factory signatures.