Port loki/#10752 to Agent

[salvacorts]

PR Description

This PR upstreams the promtail changes from grafana/loki#10752 into the Grafana Agent.

This is rather expected behavior, so no need to update the docs.

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[CLAassistant]

All committers have signed the CLA.

[tpaschalis]

LGTM, thanks for porting the changes over @salvacorts!

[alexinfoblox]

Hi @salvacorts, Is this feature available in the v0.39.0 release?
Trying to extract labels into the structed_metadata, however, discovered labels are getting added to the stream.
Config:

scrape_configs:
- job_name: kubernetes-pods
  pipeline_stages:
    - cri: {}
    - structured_metadata:
        container_image:
        app_version:
  kubernetes_sd_configs:
    - role: pod
  relabel_configs:
    - source_labels:
      - __meta_kubernetes_pod_label_app_kubernetes_io_version
      action: replace
      target_label: app_version
    - source_labels:
      - __meta_kubernetes_pod_container_image
      action: replace
      target_label: container_image

In the Loki there are duplicated labels:

And discovered labels getting added to the Label Filters

When I'm trying to use this structed_metadata in Promtail (using the latest image) with the same configuration, the feature works as expected. The extracted labels are not being added to the stream as new labels.

Why this doesn't work in Grafana-Agent?

[mattdurham]

This was only added to flow mode and it looks like you are using static mode.

[alexinfoblox]

Yeah. I'm using static mode.
Ok, will give it a try with flow mode. @mattdurham Thanks for the pointer