Support users and user roles

[ES-Alexander]

Splitting out from #3481:

• These could optionally be exposed/shared with extensions such as Cockpit
• Vehicle management features should only be doable by admins
  • These obviously need to be enforced on an API level.
  • Pirate mode could be a level higher, that's up for discussion
• Something OAuth-like?

Roles would need to factor in things like #2771.