docs(lambda): recommend a single source of truth for environment variables

[azarboon]

Issue # (if applicable)

Closes #.

This update improves the AWS Lambda component documentation in AWS CDK by recommending a single source of truth for environment variables. It addresses potential inconsistencies when defining environment variables separately in function code and infrastructure code, which can lead to mismatches during deployments.

Reason for this change

When updating a Lambda function in AWS CDK, CloudFormation applies configuration updates before code updates, which can temporarily cause environment variables to be removed or changed before the new function code is deployed. If the function executes during this period, it may fail due to missing or outdated environment variables. Defining environment variables in a single source of truth helps minimize inconsistencies and reduces the risk of deployment errors.

Description of changes

• Expanded documentation to emphasize defining environment variables centrally.
• Clarified best practices for referencing environment variables in both the handler and infrastructure code.
• Provided a recommendation to define environment variables in env.ts and reference them consistently.

Describe any new or updated permissions being added

Description of how you validated changes

The updated recommendations were tested with a standard AWS CDK deployment to confirm that environment variables remain consistent across Lambda function executions.

Ensured that the proposed approach aligns with AWS CDK’s best practices for maintainability and type safety.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.21%. Comparing base (8ca7677) to head (2945a87).
Report is 1 commits behind head on main.

Additional details and impacted files

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  Files         119      119           
  Lines        6876     6876           
  Branches     1162     1162           
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  Hits         5653     5653           
  Misses       1120     1120           
  Partials      103      103           

Flag	Coverage Δ
suite.unit	82.21% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	82.21% <ø> (ø)

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 2945a87
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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