set_aws_api_key(access_key = NULL, secret_key = NULL,
default_region = "us-east-1", error = TRUE)have_aws_key()
NULL then looks at the
AWS_ACCESS_KEY_ID system variable.NULL then looks at the
AWS_SECRET_ACCESS_KEY system variable.NULL then looks at the
AWS_DEFAULT_REGION system variable.access_key, secret_key,
and default_region