Add opensearch cluster to the reference architecture

What does this MR do and why?

The current reference architecture documentation does not mention the possibility of integrating an OpenSearch cluster. This omission may lead to confusion or missed opportunities for users who wish to enable advanced search capabilities available in GitLab Enterprise Edition (EE) or Ultimate. Including OpenSearch in the architecture—clearly marked as optional—would help clarify its role and relevance, especially for teams evaluating or planning deployments that require enhanced search features.

see #555958 (closed)

References

The goal is to add the OpenSearch cluster to this documentation : https://docs.gitlab.com/administration/reference_architectures/

Screenshots or screen recordings

Example of update for 5k architecture only, but all architectures have been updated

Before After
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How to set up and validate locally

Documentation rendering and comparison :

Architecture Before (master) After
1k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/1k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/1k_users.md
2k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/2k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/2k_users.md
3k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/3k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/3k_users.md
5k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/5k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/5k_users.md
10k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/10k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/10k_users.md
25k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/25k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/25k_users.md
50k users https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/reference_architectures/50k_users.md https://gitlab.com/gitlab-community/gitlab-org/gitlab/-/blob/555958-add-openSearch-cluster-to-the-reference-architecture/doc/administration/reference_architectures/50k_users.md

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #555958 (closed)

Edited by Lucas DRAGO

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