AWS Bedrock add Cohere Command R model support.

[maxjiang153]

AWS Bedrock Cohere Command R release link: https://aws.amazon.com/about-aws/whats-new/2024/04/cohere-command-r-r-plus-amazon-bedrock/

Cohere Command R model request and response body format is different than Cohere, so I create a new BedrockCohereCommandRChatClient client.

Here is the request body documentation: https://docs.aws.amazon.com/bedrock/latest/userguide/model-parameters-cohere-command-r-plus.html