[feature] Cli: Indicate that an account already is admin on `admin account promote`

[CherryKitten]

Is your feature request related to a problem ?

Running admin account promote for a user who already is an admin returns a return code of zero without any output indicating that the user already has admin rights. That makes it hard to determine if the command changed anything, which is impractical for automations that try to be idempotent.

Describe the solution you'd like.

Either return a non-zero exit code, output a simple message to stderr, or both.

Describe alternatives you've considered.

none (making this all uppercase feels bad, I couldn't get myself to do it)

Additional context.

meow