feat(bedrock): add support for Amazon Bedrock

[schniber]

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This pull request adds support for Amazon Bedrock as a supported provider, including:

1. New Bedrock engine implementation
2. Integration with existing config and engine selection logic
3. Support for multiple model families (Anthropic Claude, Titan, Nova, Llama, etc.)
4. Compatibility with both InvokeModel and Converse APIs
5. Handling of different response formats for various model types
6. Addition of Bedrock-specific models to the MODEL_LIST

The implementation allows for flexible configuration, including region selection, guardrails, and API authentication methods.