[BUG] Error either the bucket name or prefix in the S3 data source is duplicated

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## Describe the bug

At knowledge settings, if user inputs duplicated bucket name or prefix in S3 datasource, causes error at `cdk synth`.

If bucket name is duplicated:
- s3://hoge/fuga/
- s3://hoge/piyo/

```
Error: There is already a Construct with name 'hoge' in BedrockCustomBotStack [BrChatKbStack01JG3V7FQZYG5NGX7R87966JTT]
at Node.addChild (/codebuild/output/src1957739235/src/cdk/node_modules/constructs/src/construct.ts:447:13)
at new Node (/codebuild/output/src1957739235/src/cdk/node_modules/constructs/src/construct.ts:71:17)
at new Construct (/codebuild/output/src1957739235/src/cdk/node_modules/constructs/src/construct.ts:499:17)
at new Resource (/codebuild/output/src1957739235/src/cdk/node_modules/aws-cdk-lib/core/lib/resource.js:1:1309)
at new BucketBase (/codebuild/output/src1957739235/src/cdk/node_modules/aws-cdk-lib/aws-s3/lib/bucket.js:1:2172)
at new Import (/codebuild/output/src1957739235/src/cdk/node_modules/aws-cdk-lib/aws-s3/lib/bucket.js:1:16085)
at Function.fromBucketAttributes (/codebuild/output/src1957739235/src/cdk/node_modules/aws-cdk-lib/aws-s3/lib/bucket.js:1:16997)
at Function.fromBucketName (/codebuild/output/src1957739235/src/cdk/node_modules/aws-cdk-lib/aws-s3/lib/bucket.js:1:14937)
at /codebuild/output/src1957739235/src/cdk/lib/bedrock-custom-bot-stack.ts:353:29
at Array.forEach ()
```

If prefix is duplicated:
- s3://hoge/fuga/
- s3://piyo/fuga/

```
Error: There is already a Construct with name 'DataSourcehoge--' in BedrockCustomBotStack [BrChatKbStack01JG3V7FQZYG5NGX7R87966JTT]
at Node.addChild (/codebuild/output/src3955119784/src/cdk/node_modules/constructs/src/construct.ts:447:13)
at new Node (/codebuild/output/src3955119784/src/cdk/node_modules/constructs/src/construct.ts:71:17)
at new Construct (/codebuild/output/src3955119784/src/cdk/node_modules/constructs/src/construct.ts:499:17)
at new Resource (/codebuild/output/src3955119784/src/cdk/node_modules/aws-cdk-lib/core/lib/resource.js:1:1309)
at new DataSourceBase (/codebuild/output/src3955119784/src/cdk/node_modules/@cdklabs/generative-ai-cdk-constructs/src/cdk-lib/bedrock/data-sources/base-data-source.ts:92:1)
at new DataSourceNew (/codebuild/output/src3955119784/src/cdk/node_modules/@cdklabs/generative-ai-cdk-constructs/src/cdk-lib/bedrock/data-sources/base-data-source.ts:162:1)
at new S3DataSource (/codebuild/output/src3955119784/src/cdk/node_modules/@cdklabs/generative-ai-cdk-constructs/src/cdk-lib/bedrock/data-sources/s3-data-source.ts:98:5)
at /codebuild/output/src3955119784/src/cdk/lib/bedrock-custom-bot-stack.ts:119:16
at Array.map ()
at new BedrockCustomBotStack (/codebuild/output/src3955119784/src/cdk/lib/bedrock-custom-bot-stack.ts:116:49)
```

Also, the prefix must end with `/` , but there is no such explanation, and no error message is displayed on UI.

```
"Value error, Invalid S3 URL format (must end with a '/'): s3://hoge/hoge"
```

## To Reproduce

Steps to reproduce the behavior:

1. Go to 'bot console'
2. Click on 'create new bot'
3. Scroll down to 'S3 datasources'
4. Input duplicated:
- duplicated bucket name like `s3://hoge/fuga/` and `s3://hoge/piyo/`
- duplicated prefix like `s3://hoge/fuga/` and `s3://piyo/fuga/`
5. See errors in CodeBuild

## Screenshots


## Additional context

Add any other context about the problem here.

Start in cdk/lib/bedrock-custom-bot-stack.ts at the datasource construction around lines 116-119 and bucket handling around line 353, then reproduce both duplicate-input cases with cdk synth. Trace how the knowledge settings input reaches these entry points. Done means duplicate bucket names and prefixes no longer cause construct errors, and a prefix without a trailing slash produces a visible validation message.

Written by the indexing model from the issue text.