### Elasticsearch Version

8.x (any version where we have added support for proxies with a GCS repo)

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

N/A

### Problem Description

When configuring a GCS repository with HTTP proxy settings ([doc](https://www.elastic.co/guide/en/elasticsearch/reference/8.0/repository-gcs.html#repository-gcs-client)), we do not pass along the proxy settings to other `HttpTransportOptions` instances that we create. This can lead to timeout errors when the GCS Client tries to get a token, with the following error message:
```
Error getting access token for service account: Connect timed out, iss: ...
```

The workaround is to set the HTTP proxy settings on the JVM level rather than when defining the GCS repository, using `java.net.useSystemProxies` or `http.proxyHost`/`http.proxyPort`.

### Steps to Reproduce

[Setting up a GCS repository](https://www.elastic.co/guide/en/elasticsearch/reference/8.0/repository-gcs.html) with HTTP proxy settings (while every other non-proxied GCP call is blocked) could lead to this issue.

### Logs (if relevant)

_No response_
modules/repository-gcs/src/test/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageServiceTests.java
assertThat(e1.getMessage(), containsString("Unknown client name [gcs3]."));
            
            plugin.reload(settings2);
            
            assertThat(client11.getOptions().getProjectId(), equalTo("project_gcs11"));
            
            final Storage client21 = storageService.client("gcs1", "repo1", statsCollector);
            assertThat(client21.getOptions().getProjectId(), equalTo("project_gcs21"));
            
            assertThat(client12.getOptions().getProjectId(), equalTo("project_gcs12"));
            
            final IllegalArgumentException e2 = expectThrows(
                IllegalArgumentException.class,
                () -> storageService.client("gcs2", "repo2", statsCollector)
            );
            assertThat(e2.getMessage(), containsString("Unknown client name [gcs2]."));
            
            final Storage client23 = storageService.client("gcs3", "repo3", statsCollector);
            assertThat(client23.getOptions().getProjectId(), equalTo("project_gcs23"));
        }
    }
    public void testClientsAreNotSharedAcrossRepositories() throws Exception {
        final MockSecureSettings secureSettings1 = new MockSecureSettings();
        secureSettings1.setFile("gcs.client.gcs1.credentials_file", serviceAccountFileContent("test_project"));
        final Settings settings = Settings.builder().setSecureSettings(secureSettings1).build();
        try (GoogleCloudStoragePlugin plugin = new GoogleCloudStoragePlugin(settings)) {
            final GoogleCloudStorageService storageService = plugin.storageService;
            final Storage repo1Client = storageService.client("gcs1", "repo1", new GoogleCloudStorageOperationsStats("bucket"));
            final Storage repo2Client = storageService.client("gcs1", "repo2", new GoogleCloudStorageOperationsStats("bucket"));
            final Storage repo1ClientSecondInstance = storageService.client(