fix: remove BulkIngester backoffPolicy to prevent compound retries

BulkIngester.backoffPolicy and DispatchingTransport both used
config.maxRetries(), causing up to (maxRetries+1)^2 HTTP requests per
document: each BulkIngester per-item 429 retry issued a new bulk request
that re-entered DispatchingTransport with a fresh retry budget.

Removing backoffPolicy gives DispatchingTransport sole ownership of the
retry budget. HTTP-level 429s (whole-request) continue to be retried as
exceptions by DispatchingTransport; per-item 429s in a 200 response go
to the listener's error path (DLQ + task failure), matching pre-migration
HLRC behavior.

Author: yeikel

src/main/java/io/confluent/connect/elasticsearch/ElasticsearchClient.java

@@ -25,7 +25,6 @@
 import co.elastic.clients.elasticsearch.indices.get_mapping.IndexMappingRecord;
 import co.elastic.clients.json.JsonpMapper;
 import co.elastic.clients.json.jackson.JacksonJsonpMapper;
-import co.elastic.clients.transport.BackoffPolicy;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.Endpoint;
 import co.elastic.clients.transport.TransportOptions;
@@ -195,8 +194,6 @@ public ElasticsearchClient(
           .maxConcurrentRequests(config.maxInFlightRequests())
           .flushInterval(config.lingerMs(), TimeUnit.MILLISECONDS)
           .scheduler(this.bulkScheduler)
-          .backoffPolicy(BackoffPolicy.exponentialBackoff(
-              config.retryBackoffMs(), config.maxRetries()))
           .listener(buildListener(afterBulkCallback));
       if (config.bulkSize() > 0) {
         b.maxSize(config.bulkSize());