Add Cardinality common field

[wdhif]

What does this PR do?

Implement the card: common field to DogStatsD Datagram spec. This new field is used to override the Agent cardinality.

Description of the Change

Adds a new cardinality setting that can be either:

• Defined globally as an option
• Override on a per-metrics basis

This settings is then send as the card: common field.

Alternate Designs

Possible Drawbacks

None

Verification Process

Unit tests have been implemented to test the feature. QA has been done manually and can be found in DataDog/datadog-agent#32917.

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• PR should not have do-not-merge/ label attached.
• If Applicable, issue must have kind/ and severity/ labels attached at least.

[tobz]

What happens when this is used with an Agent version that doesn't have support for the structured card field? 🤔

[wdhif]

What happens when this is used with an Agent version that doesn't have support for the structured card field? 🤔

Hey @tobz 👋 The Agent will simply discard the unknown common field and the Agent cardinality (low by default) will be applied. I've just tested using Agent v7.60.0 and the low cardinality.

[github-actions]

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[carlosroman]

Works as expected.

[carlosroman]

/merge

[dd-devflow]

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2025-06-02 09:56:51 UTC ℹ️ Start processing command /merge

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2025-06-02 09:56:55 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in master is approximately 0s (p90).

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2025-06-02 11:30:15 UTC ℹ️ MergeQueue: This merge request was already merged

This pull request was merged directly.