system_tables.md: update index names

Изменения

https://docs.binary.picodata.io/picodata/asabirov_update_index_names/architecture/system_tables/

Версия: Picodata 24.3.0-66-g6ea360f7

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• Close #228 (closed)
• Target branch: main
• Changes should be cherry-picked to 24.2: no
• Staging: https://docs.binary.picodata.io/picodata/asabirov_update_index_names/
• Follow-up for picodata!933 (merged)