Add support to run AWS OpenSearch Serverless service (aoss)

[Rodolfo Silva]

Current behavior

I'm using the latest version of ExAWS, but I'm unable to send operations to OpenSearch. As of now, only the es service is supported by ExAWS.

index = "books"
query = %{
  "size" => 10
}

%ExAws.Operation.JSON{
  http_method: :post,
  data: query,
  path: "/#{index}/_search",
  service: :aoss,
}
|> ExAws.request(region: "us-east-1")

Expected behavior

Having support to aoss service

[Bernard Duggan]

At a minimum the service description needs to be added to priv/endpoints.exs, in particular the hostnames for it. I'd be more than happy to take a patch with that change.