Transport level retry

[l-trotta]

Adds new retry functionality to the client, configurable like so:

try (ElasticsearchClient client = ElasticsearchClient.of(e -> e
    .host(serverUrl)
    .apiKey(apikey)
    .retryConfig(r -> r
        .retryableExceptions(Set.of(SocketException.class)) // defaults to IOException.class
        .retryableStatuses(429,503) // defaults to 429, 500, 502, 503, 504
        .backoffPolicy(BackoffPolicy.constantBackoff(5000L,5)) // defaults to BackoffPolicy.noBackoff()
    )
)) 

The delegate client (Rest5Client, RestClient or any custom client) is wrapped in an instance of RetryingHttpClient, which takes care of the retrying logic according to the configuration.
This only concerns the same node the request was originally sent to, it's still the underlying client's responsibility to handle dead node logic and node selection.

[swallez]

Left some comments on implementation independence and async tasks.

Adding this to TransportOptions is an interesting choice, as it allows using different retry policies with a single transport.

[swallez]

This class should be co.elastic.transport.http.RetryingHttpClient and be independent from org.elasticsearch.client so that it can be independent of the http client implementation (see also below on exception handling)