@log_level is not fully respected

(check apply)
- [x] read [the contribution guideline](https://github.com/fluent/fluent-plugin-opensearch/blob/master/CONTRIBUTING.md)
- [ ] (optional) already reported 3rd party upstream repository or mailing list if you use k8s addon or helm charts.

#### Steps to replicate

Testing with the following match statement (note @log_level fatal):
```

@id out_opensearch
@type opensearch
@log_level fatal
scheme https
ssl_verify true
host XXXHOSTXXX
port XXXPORTXXX
user XXXUSERXXX
password XXXPASSWORDXXX
target_index_key @target_index
remove_keys @target_index
compression_level default_compression
#log_os_400_reason true

flush_interval 1s
retry_type periodic
retry_forever true
retry_wait 5s

```

#### Expected Behavior or What you need to ask

Would expect all non-fatal logs (using fatal in this example) to be suppressed.

Instead, seeing message like these:

```
NORMAL CONSOLE LOG:
2022-03-19 16:59:08 +0000 [warn]: #0 send an error event to @ERROR: error_class=Fluent::Plugin::OpenSearchErrorHandler::OpenSearchError error="400 - Rejected by OpenSearch" location=nil tag="" time=2022-03-19 16:59:06.948702500 +0000

CAPTURED FLUENTD LOGS (ie - ):
2022-03-19 16:59:08.803809500 +0000 fluent.warn: {"error":"#","location":null,"tag":"","time":1647709146,"message":"send an error event to @ERROR: error_class=Fluent::Plugin::OpenSearchErrorHandler::OpenSearchError error=\"400 - Rejected by OpenSearch\" location=nil tag=\"\" time=2022-03-19 16:59:06.948702500 +0000"}
```

#### Using Fluentd and OpenSearch plugin versions

OS version: Docker image built off ghcr.io/calyptia/fluentd:v1.14.5-debian-1.0
Bare Metal or within Docker or Kubernetes or others?: Docker image built off ghcr.io/calyptia/fluentd:v1.14.5-debian-1.0
Fluentd v1.0 or later: 1.14.5
OpenSearch plugin version: fluent-plugin-opensearch version 1.0.2