The hibernate-search-elasticsearch-aws module signs requests to AWS Elasticsearch instances, but only if we directly declare the aws secret and access keys as properties at startup.

When running on an EC2 instance its recommended to use the role provided by the EC2 instance using their provided roles that use temporary credentials https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_use-resources.html . `AWSCredentialsProvider` from the aws java sdk abstracts that in a friendly way.

It would be great if we could provide an instance of `AWSCredentialsProvider` to hibernate search at startup so that it can use that for signing the elastic search requests.