fix(apm): flatten globalLabels object

[afharo]

Summary

Related to elastic/apm-agent-nodejs#4096 (comment).

I noticed that the APM agents expect globalLabels to be key/value pairs. For this reason, when a label such as myObject.keyA: A or myObject.keyB.subKeyB: B is provided, the agents are configured as key: "myObject", value: { keyA: "A", keyB: { subKeyB: "B" } }, leading to APM reporting labels.myObject: [object Object].

This PR ensures the globalLabels object is flattened before providing it to the agents so that they apply their dot-to-underscore replacement in the key as declared in the docs.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[afharo]

/ci

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[vigneshshanmugam]

LGTM

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 0d7f6af
• Kibana Serverless Image: docker.elastic.co/kibana-ci/kibana-serverless:pr-186579-0d7f6af8a748
• Observability Deployment

Failed CI Steps

• Jest Tests #9

Test Failures

• [job] [logs] Jest Tests #9 / GlobalDataTagsTable should add new tags

Metrics [docs]

✅ unchanged

History

• 💛 Build #217029 was flaky 465d45a

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@elasticmachine merge upstream

cc @afharo