nix-daemon: Only print connection info if we have SO_PEERCRED
nix-daemon: Show name of connecting user
nix-daemon: Add trusted-users and allowed-users options

‘trusted-users’ is a list of users and groups that have elevated
rights, such as the ability to specify binary caches. It defaults to
‘root’. A typical value would be ‘@wheel’ to specify all users in the
wheel group.

‘allowed-users’ is a list of users and groups that are allowed to
connect to the daemon. It defaults to ‘*’. A typical value would be
‘@users’ to specify the ‘users’ group.