Load environment variables from SecretsManager

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**Tell us about your request**
I would love if Lambda support loading values for environment variables from SecrtesManager like ECS does. This would prevent varaibles to be visible in the Lambda console but still make them easily usable inside my function code.

**Which service(s) is this request for?**
AWS Lambda, Secretsmanager

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
see above

**Are you currently working around this issue?**
Currently, I can use environment encryption to partly solve that.

**Additional context**
N/A

**Attachments**
N/A

ファイル、テスト、エントリーポイントについては何も言及されていません。まず、必要な AWS Lambda と Secrets Manager の統合動作を明確にします。これには、権限と、Lambda コンソールでは非表示のまま値を関数コードに公開する方法が含まれます。このエンドツーエンドの動作が仕様化され、サポートされていれば完了です。

索引モデルが issue の本文から書いたものです。