Update aggregation key processor documentation to reflect new source inclusion changes

[fraseriver]

What does this PR do? What is the motivation?

ECT-3509

An additional line has been added to this documentation to reflect that @evt.source_id and @evt.integration_id are now always included in the aggregation key generation, meaning events with different sources will always have distinct aggregation keys.

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

[github-actions]

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Modified Files

• https://docs-staging.datadoghq.com/sam.fraser/update-agg-key-processor-documentation/service_management/events/pipelines_and_processors/aggregation_key

[buraizu]

Minor edit per the style guide

[fraseriver]

/merge

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2025-06-24 17:34:00 UTC ℹ️ Start processing command /merge

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2025-06-24 17:34:07 UTC ℹ️ MergeQueue: queue is disabled

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[fraseriver]

/merge -c

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[fraseriver]

/merge

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Added to the queue but the mergequeue is not enabled for now.

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[fraseriver]

/merge -c

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2025-06-24 18:03:31 UTC ℹ️ Start processing command /merge -c