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What does this PR do?

Detected java.lang.NoClassDefFoundError: com/google/gson/GsonBuilder error.

Caused: java.lang.NoClassDefFoundError: com/google/gson/GsonBuilder
        at org.datadog.jenkins.plugins.datadog.traces.DatadogTraceBuildLogic.<init>(DatadogTraceBuildLogic.java:40)
        at org.datadog.jenkins.plugins.datadog.clients.DogStatsDClient.reinitializeTracer(DogStatsDClient.java:270)
        at org.datadog.jenkins.plugins.datadog.clients.DogStatsDClient.getInstance(DogStatsDClient.java:126)
        at org.datadog.jenkins.plugins.datadog.clients.ClientFactory.getClient(ClientFactory.java:52)
        at org.datadog.jenkins.plugins.datadog.clients.ClientFactory.getClient(ClientFactory.java:84)
        at org.datadog.jenkins.plugins.datadog.publishers.DatadogCountersPublisher.execute(DatadogCountersPublisher.java:59)
        at hudson.model.AsyncPeriodicWork$1.run(AsyncPeriodicWork.java:101)
        at java.lang.Thread.run(Thread.java:745)

To fix that this PR:

• Remove the use of Gson instance in the DatadogTraceBuildLogic class.
• Build the stage_breakdown json manually.

Description of the Change

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)
• PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
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