[Documentation] Access to specialized clients is not documented

[maximekuntz]

On Read the docs, the way to get specialized clients such as IndicesClient, TransformClient... is not explained.

These clients are accessible using Elasticsearch().indices and Elasticsearch().transform... but it is not documented. It currently has to be infered from the few examples (examples: https://elasticsearch-py.readthedocs.io/en/v8.13.0/quickstart.html#deleting-an-index, https://www.elastic.co/guide/en/elasticsearch/client/python-api/current/examples.html#ex-refresh).

The documentation should explain it. At least, more examples would be very helpful.

[pquentin]

Thanks, you're right that it's a serious gap in the docs.

[pquentin]

Done in #2798