Propagate executor number data from step trace to stage trace and pipeline trace

[nikita-tkachenko-datadog]

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What does this PR do?

EXECUTOR_NUMBER environment variable is only available for specific steps, i.e. in DatadogStepListener.
Executor number has to be propagated from step to its corresponding stage, and from stage to pipeline (only for the first step in the pipeline).

https://datadoghq.atlassian.net/browse/SCV-210

Description of the Change

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[drodriguezhdez]

LGTM