system_tables.md: update system tables of plugins

Summary

• system_tables.md: update system tables of plugins

Address changes from picodata@f8832601

picodata 24.5.0-173-gf8832601

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• Close #296 (closed), #297 (closed)
• Cherry-pick to: none
• Staging:
  • ../architecture/system_tables/#_pico_plugin
  • ../architecture/system_tables/#_pico_service_route