Add support for Cluster update settings API

[Kargo]

Is your feature request related to a problem? Please describe.
I cannot complete my migration from NEST to Elastic.Clients.Elasticsearch because the Cluster update settings API is missing from the new client.

The following snippet is valid using NEST 7.17.5:

var settingsResponse = await _client.Cluster.PutSettingsAsync(
    descriptor => descriptor.Persistent(
        settings => settings.Add(
            "action.auto_create_index",
            value: false)));

Describe the solution you'd like
A cluster put settings method is available on the Elastic.Clients.Elasticsearch client with comparable syntax to the existing method from the NEST client.

Describe alternatives you've considered

• Keep using NEST client until Cluster update settings API is supported
• Implement custom client specifically to handle cluster setting updates

[flobernd]

This feature had an unmet requirement for quite some time. The missing functionality got finally implemented on specification side, but currently still misses support on the code generator.

[Kargo]

For anyone else needing this feature, it's possible to send the request manually using the Transport client and anonymous types:

var settings = new
{
    persistent = new { action = new { auto_create_index = false } }
};

await client.Transport.PutAsync<StringResponse>("/_cluster/settings", PostData.Serializable(settings));