[service] [request] support parallel invocations on a single instance

One of our highly used Node.js lambdas is mostly IO-bound, waiting for a HTTP request to complete. It would be nice if a single lambda instance can handle multiple invocations in parallel, so we can save on start-up cost, have some shared cache and not run into our quota limit as fast (we're capped at 2500 at the moment, but it's not enough).

We'd use a regular Node.js service for this, but in this case we're using Lambda@edge so we're in a bind.

The specific lambda as a auth/acl check in cloudfront before we hit a S3 origin.

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**Tell us about your request**
What do you want us to build?

**Which service(s) is this request for?**
This could be AWS Lambda itself, or integrations with other services.

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.

**Are you currently working around this issue?**
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**Additional context**
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Non vengono indicati file del repository, test o punti di ingresso; inizia verificando se questo repository di roadmap contiene codice di implementazione per la gestione delle invocazioni di Lambda@Edge. Il lavoro sarebbe completato definendo e fornendo il supporto per più invocazioni concorrenti su una singola istanza, inclusi il comportamento e i vincoli necessari per il caso d’uso di autenticazione e CloudFront indicato.

Scritto dal modello di indicizzazione a partire dal testo della issue.