feat: add service.instance.cost_center.id attribute

[Ayushi-12]

Fixes #3754

Changes

This PR takes over and refreshes #3756. It adds the service.instance.cost_center.id attribute and addresses previous feedback.

• Added service.instance.cost_center.id to the registry.
• Updated service.instance entity.
• Added changelog entry.
• Regenerated all documentation via make fix.

Supersedes #3756. Fixes #3754.

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Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Links to prototypes or existing instrumentations (when adding or changing conventions)
• Disclose AI usage, see OTel GenAI policy:
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Footnotes

1. Yes, I can answer maintainer questions about the content of this PR without using AI. ↩

[joaopgrassi]

Is it really an id? Was name considered? I wonder if that's the best way forward. Sounds weird to call it id when I imagine usually we will have the name of the cost center.

[Ayushi-12]

We could likely have both.
cost_center IDs are also relevant as they represent a direct mapping to some account ID of a cloud provider.

[joaopgrassi]

I see. To me name sounds the most likely thing we will see. I wonder if we should discuss it more, find more examples. I particularly find id for cost center a bit unknown of. I always see it as a "human-friendly" string, usually the name of a department or smt.

Having both is fine, I just then think we need to make sure it's clear when both/or not should be populated.

[joaopgrassi]

In Dynatrace we have for example this guidance: https://docs.dynatrace.com/docs/manage-your-costs/allocate/plan-and-set-up#choose-an-allocation-model

[Ayushi-12]

Let's discuss this over slack. I like the idea of having both, but I would want more opinions for narrowing down the definition.

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