Support rerank on aws

[billytrend-cohere]

Fixes #200

This PR introduces a new endpoint, rerank, to the AWS utility functions. The changes are as follows:

• The nonStreamedResponseParser object in src/aws-utils.ts now includes a new property, "rerank": serializers.RerankResponse,.
• The AwsEndpoint type in src/aws-utils.ts has been updated to include the new rerank endpoint.
• The models object in src/test/bedrock-tests.test.ts has been extended with a new property, rerank: "cohere.rerank-v1", for both the bedrock and sagemaker platforms.
• The getEndpointFromUrl function in src/aws-utils.ts has been removed.