Support retry with exponential backoff #1370
Description
When bulk importing large datasets, e.g., with elasticsearch-model Article.limit(100000).import, the server can easily become overloaded and respond with 429 Too Many Requests. While elasticsearch-ruby supports retries with retry_on_failure, there is no pause between retries, making them not very useful for dealing with the rate limitation. Ideally, retry should support delays with exponential backoff to adjust its request rate to what is supported by the server.