Admin user should be possible to toggle admin privileges

[dmitriy-borzenko]

Requirements

• Admins have access to dataset flows and settings as if they were owners of that dataset
• It should be possible to toggle admin privileges ON and OFF in UI to see things as an ordinary user
• When Admin user logs in this toggle should be OFF by default
  • This guard should also prevent us from navigating to admin-only views by direct links
• There should be a clear indication for actions that use admin privileges. Datasets, tabs, and settings that would've been not available to the user if they were not an admin should be clearly marked, to make admins think twice before making any changes using their elevated privileges