feat: ADMIN message type

[JarbasAl]

is_admin property has been stubbed for each client in db but is not used,

• add ADMIN HiveMessage type,
• when sent from master -> client , can change any of the values in identity file
  • port / host -> change device to a different server
  • key / password -> rotate credentials for security
  • is_admin state -> revoke/grant permission to emit ADMIN messages
• when sent from client -> master:
  • only allowed if client is_admin
  • list connected clients
  • CRUD operations on db

additionally admin clients in db should have different default allowed_messages at creation time (eg, allow system.reboot and system.shutdown)