Update AlgoliaUnreachableHostException to OperationTimeout

- Algolia Client Version: 2.5.0 (I see that 3.0 was released 3 days ago, not sure if that resolves this)
- Language Version: Python 3.9.7

### Description

Client throws `algoliasearch.exceptions.AlgoliaUnreachableHostException`: Unreachable hosts during `replace_all_objects` operation. The issue was not that hosts were unreachable but that the operation was timing out. I fixed the problem by setting `readTimeout` to 100:

```
client = SearchClient.create(algolia_application_id, algolia_api_key)
index = client.init_index(algolia_index)
request_options = {
"readTimeout": 100
}
index.replace_all_objects(records, request_options)
```

A timeout should produce a timeout error. Unreachable is misleading.

### Steps To Reproduce

See description.
Use `replace_all_objects` on a sufficiently big index. Mine was 6393 rows and 10+ columns some with significant text blocks.

まず、Python クライアントにおける replace_all_objects のタイムアウト処理を追跡し、失敗が AlgoliaUnreachableHostException にどのようにマッピングされるかを確認します。十分に大きなインデックスで操作を再現し、その後、読み取りタイムアウトでは OperationTimeout が報告され、実際に到達不能なホストでは引き続きホスト例外が報告されることを検証します。

索引モデルが issue の本文から書いたものです。