Add Bedrock + Sagemaker support

[billytrend-cohere]

This PR adds AWS integration to the Cohere client.

• It adds a new src/aws-utils.ts module that provides utility functions for working with AWS.
• New AwsClient, BedrockClient, and SagemakerClient classes are added in src/AwsClient.ts, src/BedrockClient.ts, and src/SagemakerClient.ts respectively.
• The package.json file is updated to include new dependencies required for AWS integration, such as @aws-sdk/client-sagemaker, @aws-sdk/credential-providers, @aws-sdk/protocol-http, and @aws-sdk/signature-v4.
• The test.yml file is updated to include AWS-related environment variables.
• The src/index.ts file is modified to export the new BedrockClient and SagemakerClient classes.
• New test files src/test/aws-util-tests.test.ts and src/test/bedrock-tests.test.ts are added to test the AWS integration.

[billytrend-cohere]

waiting on fern feature to make the tests pass but have verified that they pass locally