Update cross org api docs to include auth headers

[abe-lin-dd]

What does this PR do? What is the motivation?

When writing synthetic tests for cross org, we noticed that the
documentation incorrectly stated that api and app key need to be passed in as query parameters.

The app and api key need to be passed in as request headers for the cross org api to work properly. See linked synthetic test PR for usage of these headers.

Merge instructions

Merge readiness:

• Ready for merge

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/merge

Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/abe-lin/update-cross-org-auth-headers/account_management/org_settings/cross_org_visibility_api

[abe-lin-dd]

/merge

[dd-devflow]

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2025-03-07 18:29:46 UTC ℹ️ Start processing command /merge

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2025-03-07 18:32:06 UTC ⚠️ MergeQueue: This merge request was unqueued

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