Bulk ingester retry policy

[l-trotta]

Adds retry logic to the bulk ingester, allowing it to to retry operations that failed with error 429 (too many requests), hoping that the error will recover and the request will go through. Users can configure the desired backoff policy using the backoffPolicy() method in the bulk ingester builder, which will look like this:

BulkIngester ingester = BulkIngester.of(b -> b
            .client(client)
            ...
            .listener(listener)
            .flushInterval(1000, TimeUnit.MILLISECONDS)
            .backoffPolicy(BackoffPolicy.constantBackoff(50L, 8)) 

This is an example of constant backoff, meaning the single failed operation will be retried 8 times every 50 milliseconds.

[swallez]

Sounds good overall, except for some potentially costly list operations. Bulk ingestion is used in high load contexts where performance is critical, and the number of operations per request (and thus list size) can be large.

[swallez]

LGTM. Great stuff!