[extension/header_setter] Expose auth attributes

[jenrik]

Description

Allow settings header values based on authentication attributes

Testing

• Ran test suite, and added tests for the new code

Documentation

Update extension README to explain from_attribute

[atoulme]

Please add a changelog

[atoulme]

Passes my summary review. Codeowners please review.

[atoulme]

@VihasMakwana please review.

[VihasMakwana]

LGTM

[VihasMakwana]

@atoulme it's good to go now.

[KimMJ]

Hi. I have question on this change. I thought it resolves #34257 but seems it is not related. Do I understand it correctly? Actually I wanted to set header from attributes so tested dev environment with 0.122.0 docker image, and it was failed. otelcol get panic and restarted

I added tenant id from otelcol A

      attributes:
        actions:
          - action: insert
            key: tenant_id
            value: "attribute_tenant"

and tried to set header from this in otelcol B

    headers_setter:
      headers:
        - action: insert
          key: X-Scope-OrgID
          from_attribute: tenant_id
          default_value: unknown

And it didn't work.

[jenrik]

Authorization attributes and metric/trace attributes are unfortunately not the same, and are very confusingly named. I had to dig through the source code to understand it.

[dehaansa]

Is there a way to make this work with a batchprocessor in the pipeline? From what I see in the code for batchprocessor it only preserves metadata from the ctx Info object's Metadata map, not the Auth map.