[Amazon Bedrock] Add AmazonBedrockChatGenerator

[julian-risch]

In addition to the recently merged AmazonBedrockGenerator #153, we need a AmazonBedrockChatGenerator supporting ChatMessages as format.

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1. The change is documented with docstrings and was merged in the main branch
2. Integration tile on https://github.com/deepset-ai/haystack-integrations was updated
3. Docs at https://docs.haystack.deepset.ai/ were updated
4. Notebooks on https://github.com/deepset-ai/haystack-cookbook were updated (if needed)
5. New package version declares the breaking change and package has been released on PyPI