S3 Vector L2 CDK Constructs

## Description

We want to add L2 CDK Constructs for S3 vectors: Index, VectorBucket, VectorBucketPolicy

This is part of the effort to move the Bedrock Knowledge Base construct to the bedrock alpha package

https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/AWS_S3Vectors.html
https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3-vectors.html

We have an existing implementation for these here: https://github.com/awslabs/generative-ai-cdk-constructs/tree/main/src/cdk-lib/s3vectors

## Roles

| Role | User
|---------------------|------------------------------
| Proposed by | @krokoko
| Author(s) | @krokoko
| API Bar Raiser | @alias
| Stakeholders | @alias, @alias, @alias

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

## Workflow

- [x] Tracking issue created (label: `status/proposed`)
- [ ] API bar raiser assigned (ping us at [#aws-cdk-rfcs](https://cdk-dev.slack.com/archives/C025ZFGMUCD) if needed)
- [ ] Kick off meeting
- [ ] RFC pull request submitted (label: `status/review`)
- [ ] Community reach out (via Slack and/or Twitter)
- [ ] 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`)

---

> 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.

Start by reading the AWS CloudFormation S3 Vectors and Amazon S3 Vectors documentation linked in the issue, then compare the existing implementation in generative-ai-cdk-constructs/src/cdk-lib/s3vectors. Follow the RFC checklist and confirm the API design and implementation status; done means the proposed constructs have completed the listed approval and implementation workflow.

Written by the indexing model from the issue text.