DRAFT: Replacing Elasticsearch by OpenSearch

[psaiz]

:heart: Thank you for your contribution!

Description

If I'm not mistaken, InvenioILS uses OpenSearch instead of Elasticsearch. I'm updating the documentation accordingly.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [X] I'm aware of the code of conduct.
• [ ] I've created logical separate commits and followed the commit message format.
• [ ] I've added relevant test cases.
• [ ] I've added relevant documentation.
• [ ] I've marked translation strings (for relevant code).
• [ ] I've followed the CSS/JS and React guidelines (for relevant code).
• [ ] I've followed the web accessibility guidelines (for relevant code).
• [ ] I've followed the user interface guidelines (for relevant code).
• [ ] I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
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[ntarocco]

Fixed here because I cannot push to this branch :)