Update dual shipping instructions for CI Visibility API

[albertvaka]

What does this PR do?

Add a section about how to configure CI Visibility for dual shipping.

DO NOT MERGE: There's no Agent nor tracer version released that uses this yet.

Motivation

API added in https://github.com/DataDog/datadog-agent/pull/12271

Additional Notes

We might use it for other products in the future, but the first user will be CI Visibility so I've documented it like that.

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Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/albertvaka/dual-shipping-for-evp-proxy/agent/guide/dual-shipping