ref(tests): use constants in ai integration tests and add missing ones

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Note

The pull request "ref(tests): use constants in ai integration tests and add missing ones" was created by @nicohrubec but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

While working on the gen_ai.request.messages rename I noticed that we hardcode all the attributes in our ai integration tests (both node and cloudflare), meaning that we currently need to change each individual test just to rename one attribute name. This PR refactors this to use the attributes from our gen-ai-attributes.ts. I also added some missing entries for attributes that we currently hardcode in the integrations.

[linear]

JS-1541

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A PR closing this issue has just been released 🚀

This issue was referenced by PR #18945, which was included in the 10.37.0 release.