Add support for Amazon Bedrock Citations Option within DocumentBlock object

### Description

## Description

The AI SDK should support the new AWS Bedrock Citations API feature that was recently added to the platform. This feature is crucial for improved PDF parsing capabilities, particularly for image-based PDFs, and provides native citation generation for models that support it (such as Claude/Anthropic).

### Background

AWS Bedrock now supports a `citations` configuration option in the `DocumentBlock` as documented in the [[AWS API Reference](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_DocumentBlock.html)](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_DocumentBlock.html). This feature enables:

1. **Enhanced PDF Processing**: Bedrock can natively scan image PDFs for supported models
2. **Automatic Citation Generation**: The model can generate citations that reference source documents
3. **Better Document Understanding**: Improved contextual understanding of document content

### Proposed Implementation

The citations configuration should be added as an optional parameter with the following structure:

```typescript
export interface BedrockDocumentBlock {
  document: {
    format: BedrockDocumentFormat;
    name: string;
    source: {
      bytes: string;
    };
    citations?: {
      enabled: boolean;
    };
  };
}
```

The implementation can follow the same pattern as the existing `getCachePoint` function:

```typescript
function getCachePoint(
  providerMetadata: SharedV2ProviderMetadata | undefined,
): BedrockCachePoint | undefined {
  return providerMetadata?.bedrock?.cachePoint as BedrockCachePoint | undefined;
}

function getCitationsConfig(
  providerMetadata: SharedV2ProviderMetadata | undefined,
): BedrockCitationsConfig | undefined {
  return providerMetadata?.bedrock?.citations as BedrockCitationsConfig | undefined;
}
```

This can then be utilized when adding valid `BedrockDocumentBlock` to `bedrockContent` or in a similar way to `getCachePoint`

```typescript
bedrockContent.push({
  document: {
    format: getBedrockDocumentFormat(part.mediaType),
    name: generateDocumentName(),
    source: { bytes: convertToBase64(part.data) },
    citations: getCitationsConfig(providerOptions),
  },
});
```

### Benefits

- **Improved PDF Support**: Native handling of image-based PDFs without external OCR
- **Better Attribution**: Automatic citation generation for document-based responses
- **Enhanced Accuracy**: Models can better reference specific parts of source documents
- **Future-Proofing**: Aligns with AWS Bedrock's roadmap and capabilities

### References

- [[AWS Bedrock DocumentBlock API Reference](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_DocumentBlock.html)](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_DocumentBlock.html)
- [[Amazon Bedrock's New Citations API and PDF Support](https://stackpioneers.com/2025/07/01/amazon-bedrocks-new-citations-api-and-pdf-support/#overview-of-the-citations-api)](https://stackpioneers.com/2025/07/01/amazon-bedrocks-new-citations-api-and-pdf-support/#overview-of-the-citations-api)

This feature is particularly valuable for applications that work with complex documents, research materials, and scenarios where source attribution is critical.

### AI SDK Version

- AI: Latest
- AI/Bedrock: Latest

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Labels: ai/provider, support, provider/amazon-bedrock
State: closed