Docs: Add OpenSearch cluster to the reference architectures

• Start this issue's title with Docs: or Docs feedback:.

Problem to solve

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.

Further details

Adding OpenSearch to the reference architecture documentation would help clarify deployment options for users of GitLab Enterprise Edition (EE) and Ultimate who wish to enable advanced search capabilities.

This addition would benefit:

• Infrastructure and DevOps engineers designing scalable GitLab deployments.
• Solution architects evaluating optional components based on feature requirements.
• Technical decision-makers comparing editions and planning for future extensibility.
• Allows you to point to an architecture scheme close to the one in production

Proposal

Add a new row to the reference architecture table to include OpenSearch, marked as optional, with a note that it is only required when Advanced Search is enabled in Enterprise Edition (EE) or Ultimate:

Update the architecture diagram to visually include OpenSearch as an optional component—using a legend to clarify its optional nature and specific use case:

Who can address the issue

I can do it as my first gitlab community contribution

Other links/references

https://docs.gitlab.com/administration/reference_architectures