Serverless ElastiCache L2 Construct

## Description

Amazon ElastiCache is an AWS web service that makes it easy to set up, manage, and scale a distributed in-memory data store or cache environment in the cloud. It provides a high-performance, scalable, and cost-effective caching solution. At the same time, it helps remove the complexity associated with deploying and managing a distributed cache environment.

The L2 Construct delivers a high-level abstraction over AWS Serverless ElastiCache (together with its needed constructs: User and UserGroup) using AWS CDK, aimed at simplifying the development of Serverless Redis/Valkey or Memcached caching processes with sensible defaults and extensibility. It enables developers to quickly provision secure, performant caching layers without needing to dive into the low-level configuration details of ElastiCache. The construct encapsulates best practices around VPC networking, subnet group configuration, encryption, and IAM policies, significantly reducing the time it takes to get a cache system up and running in production-ready environments.

## Roles

| Role | User
|---------------------|------------------------------
| Proposed by | @maramure
| Author(s) | @maramure
| API Bar Raiser | @otaviomacedo
| Stakeholders | @rambow, @praneetap

> See [RFC Process](https://github.com/aws/aws-cdk-rfcs#rfc-process) for details

## Workflow

- [x] Tracking issue created (label: `status/proposed`)
- [x] API bar raiser assigned (ping us at [#aws-cdk-rfcs](https://cdk-dev.slack.com/archives/C025ZFGMUCD) if needed)
- [x] Kick off meeting
- [x] RFC pull request submitted (label: `status/review`)
- [ ] Community reach out (via Slack and/or Twitter)
- [x] API signed-off (label `status/api-approved` applied to pull request)
- [ ] Final comments period (label: `status/final-comments-period`)
- [ ] Approved and merged (label: `status/approved`)
- [ ] Execution plan submitted (label: `status/planning`)
- [ ] Plan approved and merged (label: `status/implementing`)
- [ ] Implementation complete (label: `status/done`)

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> Author is responsible to progress the RFC according to this checklist, and
apply the relevant labels to this issue so that the RFC table in README gets
updated.