Make retry_host_predicate Configurable or Remove Default from Retry Policy

Currently, Envoy Gateway sets the following retry host predicate by default in all [retry policies](https://github.com/envoyproxy/gateway/blob/521b78b6efdcd13ebe3fe14c06c45681a84ef97c/internal/xds/translator/route.go#L619):

```json
"retry_host_predicate": [
{
"name": "envoy.retry_host_predicates.previous_hosts",
"typed_config": {
"@type": "type.googleapis.com/envoy.extensions.retry.host.previous_hosts.v3.PreviousHostsPredicate"
}
}
]
```

This behavior is hardcoded and cannot be disabled or customized by users.
In the case of clusters with only a single host, this predicate causes retries to fail immediately, since there are no other hosts to select from.

### Request:

Please consider making `retry_host_predicate` configurable.
Alternatively, remove it from the default retry policy unless explicitly set by the user.

Thanks