[Lambda][CloudWatch] Memory Usage as a CloudWatch Metric

### Community Note

* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue or have submitted a pull request, please leave a comment

**Tell us about your request**
Adding Lambda memory usage as a CloudWatch metric would enable users to create alarms on memory usage, allowing proactive adjustments to memory allocation before encountering errors. It would also simplify monitoring this critical parameter by making memory usage directly visible in the Monitoring section of the Lambda console.

This enhancement would improve visualization of memory usage and facilitate better handling of memory-related issues (e.g., insufficient memory) before they result in errors.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Currently, there are no direct metrics for memory usage in CloudWatch. Users must rely on CloudWatch Logs Insights queries to extract memory usage data, which adds complexity and is less user-friendly.

**Are you currently working around this issue?**
To monitor memory usage, we need to navigate to Monitoring, then CloudWatch Logs, and execute a Logs Insights query such as:
```
filter @type = "REPORT"
| stats max(@memorySize / 1000 / 1000) as provisionedMemoryMB,
min(@maxMemoryUsed / 1000 / 1000) as smallestMemoryRequestMB,
avg(@maxMemoryUsed / 1000 / 1000) as avgMemoryUsedMB,
max(@maxMemoryUsed / 1000 / 1000) as maxMemoryUsedMB,
provisionedMemoryMB - maxMemoryUsedMB as overProvisionedMB
```
Alternatively, memory usage information can be found in "Recent invocations" and "Most expensive invocations in GB-seconds (memory assigned * billed duration)." However, these methods are not the most user-friendly or efficient for monitoring memory usage.

**Additional context**
N/A

**Attachments**
N/A

Nell’issue non vengono menzionati file del repository, test o punti di ingresso del codice. Inizia esaminando le funzionalità delle metriche di AWS Lambda e CloudWatch descritte qui, quindi determina la definizione della metrica e il percorso di integrazione necessari. Il lavoro è completato quando l’utilizzo della memoria di Lambda è disponibile come metrica CloudWatch e può essere utilizzato per il monitoraggio e gli allarmi.

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