[APM Onboarding] Use creation timestamp and UID of DatadogAgent as env vars for APM Telemetry KPIs (#1157)

[fanny-jiang]

What does this PR do?

Cherry-pick #1157

Motivation

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Additional Notes

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Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

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Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 59.56%. Comparing base (70db137) to head (b5bda0b).

Additional details and impacted files

@@           Coverage Diff           @@
##             v1.6    #1164   +/-   ##
=======================================
  Coverage   59.56%   59.56%           
=======================================
  Files         174      174           
  Lines       21565    21565           
=======================================
  Hits        12845    12845           
  Misses       7941     7941           
  Partials      779      779           

Flag	Coverage Δ
unittests	59.56% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ontrollers/datadogagent/component/agent/default.go	0.00% <0.00%> (ø)

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