feat: update to otel semconv 1.40.0

[epbensimpson]

Description

Updates KafkaFlow.OpenTelemetry to the OTEL Semantic Conventions 1.40.0 (current version at time of writing).

https://github.com/open-telemetry/semantic-conventions/blob/v1.40.0/docs/messaging/kafka.md

This contains some breaking changes to attribute names due to the unstable nature of the spec.

Implements #470

Summary of changes

Removed

Attribute	Reason
peer.service	Contained the bootstrap server list, which does not represent the broker that handled a given message

Renamed

Old	New	Where
messaging.operation = "publish"	messaging.operation.type = "send" + messaging.operation.name = "publish"	Producer
messaging.source.name	messaging.destination.name	Consumer
messaging.kafka.consumer.group	messaging.consumer.group.name	Consumer
messaging.kafka.message.offset	messaging.kafka.offset	Both
messaging.kafka.source.partition	messaging.destination.partition.id	Consumer
messaging.kafka.destination.partition	messaging.destination.partition.id	Producer

Added

Attribute	Where	Notes
messaging.client.id	Consumer	Set to ConsumerContext.ConsumerName — closest available proxy for the Kafka client ID, which is not exposed by IConsumerContext
messaging.kafka.message.tombstone = true	Both	Only emitted when message value is null
messaging.message.body.size	Consumer	Only emitted when the message value is still byte[] (i.e. before deserialization middleware has run)
error.type	Both	Emitted in error handlers only; value is the exception's fully-qualified type name

Bug fix

messaging.kafka.message.key: the consumer previously always emitted this tag (empty string for null keys, with an unsafe cast to byte[]), and the producer emitted the raw
object. Both now share a FormatMessageKey helper that UTF-8 decodes byte[] keys, calls ToString() on other types, and omits the tag entirely when the key is null.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have made corresponding changes to the documentation

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[simaoribeiro]

The messaging.operation.type tag name for consumer is being set with the value process instead of receive like you wrote in your PR description

[epbensimpson]

Ah I think I made that change after raising the PR, I spotted the list of well-known values and process seems like the more appropriate value here:

Value	Description
process	One or more messages are processed by a consumer.
receive	One or more messages are requested by a consumer. This operation refers to pull-based scenarios, where consumers explicitly call methods of messaging SDKs to receive messages.

I'll update the PR description

[simaoribeiro]

I would put this consumer specific attribute in the consumer handler, just like the process attribute, or else move all consumer/producer attributes to this class. What's your opinion @brmagadutra @joelfoliveira ?

[epbensimpson]

I may be missing something but I'm fairly sure all of the attribute keys are defined here? Except for messaging.system which is still inline in SetGenericTags (and could probably be moved for consistency)

The only strings defined in the Producer/Consumer handlers are for tag values, not keys.