Error when activating a machine as a user is confusing

[ezekg]

As a license user, if you forget to provide the owner relationship for the machine, the error message is too general. It should be more specific, communicating that the failure is because the user doesn't have permission to activate a machine that isn't theirs (because they're not the license owner).

See: https://github.com/keygen-sh/keygen-api/blob/master/app/policies/machine_policy.rb#L53