kafkaexporter: inject client metadata into Kafka message headers

[axw]

Component(s)

exporter/kafka

Is your feature request related to a problem? Please describe.

I would like to propagate client metadata (e.g. a tenant ID) all the way to our backend. We have Kafka in the middle of our pipeline, like this:

flowchart LR
  otlpreceiver --> kafkaexporter
  kafkaexporter --> Kafka
  Kafka --> kafkareceiver
  kafkareceiver --> otlpexporter
  otlpexporter --> backend

Loading

otlpreceiver has include_metadata configuration which instructs it to record gPRC metadata (HTTP headers) as client metadata. This can be injected into out going requests using https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/extension/headerssetterextension

Neither kafkareceiver nor kafkaexporter currently propagate client metadata.

Describe the solution you'd like

Add configuration to kafkaexporter for adding message headers based on client metadata, similar to headerssetterextension.

See also #39129

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• exporter/kafka: @pavolloffay @MovieStoreGuy @axw

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[marclop]

I'd love to pick up this work and perhaps #39129 too since they're pretty closely related.

[crobert-1]

Issue filed by code owner, removing needs triage

[marclop]

Linked PR is now ready for review.