Adding cards to the index pages of RtD

[jacoguzo]

Description

Start with a short description of what the PR does and how this is a change from
the past.

Changing index pages of RtD to have a cleaner interface.

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Tests

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Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[melissawm]

Love it! My suggestion would be to have 2 cards per row, instead of 3. This would make the text flow a bit better, I think.