[bug]: objectIDKey configuration not longer working

### Description

The [objectIDKey](https://www.algolia.com/doc/api-reference/api-methods/save-objects/#method-param-objectidkey) seems not longer work.

In my case my documents have a `id` or `uuid` as primary field but in the abstraction https://github.com/schranz-search/schranz-search whatever field somebody want can be defined as identifier field. For that I currently used the `objectIDKey` configuration.

Is there another way may on createIndex to define the primary / identifier field?

### Client

Search

### Version

v4.4.1

### Relevant log output

_No response_

Start by tracing how objectIDKey is handled in the PHP client's save-objects flow and how createIndex exposes identifier configuration. Reproduce the reported behavior with documents keyed by id or uuid on v4.4.1, then verify the supported configuration and expected behavior. Done means the identifier setting works as documented or the supported alternative is clearly documented.

Written by the indexing model from the issue text.