fix: skip API key retrieval when extension is running

[purple4reina]

Clone of #680
Just to run the tests, do not merge!

Move getAPIKey call to avoid unnecessary Secrets Manager calls when Datadog Lambda Extension is present, preventing Signature expired errors in provisioned concurrency environments.

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Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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• This PR's description is comprehensive
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