[Otlphttp Exporter] Enable metadata population in otlphttp when sending_queue is enabled

[gizas]

Description

Feature: The enablement of the sending_queue in the configuration of the otplhttp exporter does not preserve the metadata information of the initial context.

This pr introduces a new configuration called metadata_keys that will be used in the exporter config

Testing

• Added partionetr_test

• Built my local otlp exporter

Configuration of otlphttp:

otlphttp:
        endpoint: https://endpoint.invalid/_otlp
        timeout: {{ .http_request_timeout | quote }}
        sending_queue:
          enabled: true
          num_consumers: {{ .concurrentRequests }}
          wait_for_result: false
          block_on_overflow: true  # false = data loss on queue full
          sizer: requests
          queue_size: {{ .queuedRequests }}
        metadata_keys:
          - project-id

See "ProjectID":"local" that is populated below in my logs

{"log.level":"info","@timestamp":"2025-11-06T15:51:49.955Z","message":"ecpRoutingRoundTripper: after URL modification","resource":{"cloud.availability_zone":"local","k8s.namespace.name":"motel-index-collector","k8s.node.name":"hotel-worker2","k8s.pod.name":"motel-index-collector-local-58484b67c8-l4vrt","k8s.pod.uid":"1a8f6fad-91b6-413a-a929-6d004ca489b3","orchestrator.cluster.name":"default","orchestrator.deploymentslice":"","orchestrator.environment":"default","service.instance.id":"ecf43bce-5aac-444c-b244-8871bbf2d69a","service.name":"motel-index-collector","service.version":"git"},"otelcol.component.id":"ecproutingmiddleware","otelcol.component.kind":"extension","final_url_host":"local.es.svc.cluster.local:9200","final_url_scheme":"http","final_url":"[http://local.es.svc.cluster.local:9200/_otlp/v1/metrics","final_host":"","ProjectID":"local","header_count":6,"ecs.version":"1.6.0"}](http://local.es.svc.cluster.local:9200/_otlp/v1/metrics%22,%22final_host%22:%22%22,%22ProjectID%22:%22local%22,%22header_count%22:6,%22ecs.version%22:%221.6.0%22%7D)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.25%. Comparing base (a6a1766) to head (00a18f3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14139   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files         657      658    +1     
  Lines       41068    41115   +47     
=======================================
+ Hits        37888    37932   +44     
- Misses       2176     2178    +2     
- Partials     1004     1005    +1     

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[gizas]

@bogdandrutu (sorry for direct ping) did you by any chance have time to review above pr? Do I have to add someone else specific?

Any hint will be really appreciated

[axw]

Should this be in exporterhelper.QueueBatchConfig, so (a) it's kept close to the related batching config, and (b) it's available to all exporters?