Rosik/misc

• access_control.md: hide implementation details
• access_control.md: minor renaming

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• Close https://git.picodata.io/picodata/picodata/picodata/-/issues/560
• Target branch: main
• Changes should be cherry-picked to 24.2: yes
• Staging: https://docs.binary.picodata.io/picodata/rosik_misc/