Bedrock API key.
Enables authentication using Bedrock API keys instead of standard AWS credentials. When provided, the key is set as the AWS_BEARER_TOKEN_BEDROCK environment variable.
See: https://docs.aws.amazon.com/bedrock/latest/userguide/api-keys-use.html
If not provided, will be read from AWS_BEARER_TOKEN_BEDROCK environment variable.
If both an API key and AWS credentials are present, the API key takes precedence.
