### Elasticsearch Version

8.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

win10

### Problem Description

I am using GCP plugin with Elasticsearch 8.0 and it seems that the settings that are specified in the documentation [here](https://www.elastic.co/guide/en/elasticsearch/reference/8.0/repository-gcs.html) are not available to use in Elasticsearch. I have further gone into investigation to investigate GCS repository plugin and below are my observations:
The settings are declared in GoogleCloudStorageClientSettings.java class [here](https://github.com/elastic/elasticsearch/blob/690bac5dc375b5a1e8f6b3b091d38ee6cdeb0b05/modules/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageClientSettings.java#L101) but they are not loaded in the implementation getSettings() method [here](https://github.com/elastic/elasticsearch/blob/690bac5dc375b5a1e8f6b3b091d38ee6cdeb0b05/modules/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStoragePlugin.java#L66).
Due to this elasticsearch.bat is throwing error and exiting instead of starting Elasticsearch.

### Steps to Reproduce

1. Specify the below settings in elasticsearch.yml:
gcs.client.default:
  proxy.host: "abc.com"
  proxy.port: 80
  proxy.type: "http"
2. Start elasticsearch.bat and this will generate **java.lang.IllegalArgumentException: unknown setting [gcs.client.default.proxy.host] please check that any required plugins are installed, or check the breaking changes documentation for removed settings** followed by exiting the bat script.

### Logs (if relevant)

@KarenSumner @liladler Could you please help prioritize of fixing this bug?
<img width="947" alt="elastic_bug" src="https://user-images.githubusercontent.com/100778274/156373380-203706a9-ad1d-423d-a51f-4c40189f6c92.PNG">
 
modules/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStoragePlugin.java
final GoogleCloudStorageService storageService;
    public GoogleCloudStoragePlugin(final Settings settings) {
        this.storageService = createStorageService();
        
        reload(settings);
    }
    
    protected GoogleCloudStorageService createStorageService() {
        return new GoogleCloudStorageService();
    }
    @Override
    public Map<String, Repository.Factory> getRepositories(
        Environment env,
        NamedXContentRegistry namedXContentRegistry,
        ClusterService clusterService,
        BigArrays bigArrays,
        RecoverySettings recoverySettings
    ) {
        return Collections.singletonMap(
            GoogleCloudStorageRepository.TYPE,
            metadata -> new GoogleCloudStorageRepository(
                metadata,
                namedXContentRegistry,
                this.storageService,