system_tables.md: add system tables of plugins

Изменения

1. 7e32cdca: address changes from picodata!928 (merged) — picodata@26b11774
2. 07904455: address changes from picodata!948 (merged) — picodata@6a39a360

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• Close #236 (closed)
• Changes should be cherry-picked to 24.2: no
• Staging: https://docs.binary.picodata.io/picodata/asabirov_add_plugins_system_tables/architecture/system_tables/