Retry on conflict should have its own config

Hi, currently retry on conflict value is coupled to max.inflight.request, meaning that if we set max.inflight.request to 1, then the retry on conflict value will be 1. And it is capped at 3. Is there any reasoning why retry on conflict doesn't have their own config instead of coupling it with the inflight request and capped it to 3 ?

```
if (config.indexWriteMethod() == IndexWriteMethod.UPSERT) {
bulkOperation = BulkOperation.of(b -> b.update(u -> u.id(documentId)
.index(indexName)
.routing(routing)
.document(binaryData)
.upsert(binaryData)
.docAsUpsert(true)
.retryOnConflict(Math.min(config.maxInFlightRequests(), 3))));
```

I can help to make a PR if this is not intended.

Thank you

Start at the UPSERT branch shown in the issue, then trace how max.inflight.request is defined and passed through the connector configuration. Done means retryOnConflict is controlled by its own configuration rather than Math.min(config.maxInFlightRequests(), 3), with the resulting behavior covered by the relevant project tests.

索引モデルが issue の本文から書いたものです。