Use the official opensearch-php library

Problem/Motivation

At the moment we are using a Guzzle client to integrate with Opensearch. If we use the offical opensearch-php we can avoid duplicating the work of keeping it up to date with API deprecations etc. (e.g. 🐛 Fix compatibility with OpenSearch 3 Active )

See https://github.com/opensearch-project/opensearch-php

I am a maintainer of the library and the search_api_opensearch module and am happy to help with this.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes