refactor: merge _pico_role to _pico_user

Summary

Merge '_pico_role' to '_pico_user'

• Deleted '_pico_role' table
• Added new field 'type' to '_pico_user' table format

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• Close #403 (closed)
• Target branch: master
• Changes should be cherry-picked to 24.1: no
• Docs follow-up: docs#198 (closed)