Add stage breakdown to Jenkins Build/Pipelines traces.

[drodriguezhdez]

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What does this PR do?

This PR adds the Stage breakdown information for Jenkins Build/Pipelines traces.

Description of the Change

The root span includes the tag _dd.ci.stages with the array of all stages (name, duration) serialized in JSON.

Alternate Designs

Possible Drawbacks

Verification Process

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
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[mgarabed]

Does this package need to be added to pom.xml?

[drodriguezhdez]

Not needed because is inherited by the jenkins dependencies