Add 8.8.8.8 DNS to pifi connections by default.

[MoffKalast]

This is still unconfirmed but it seems that in some cases the following may happen on robot setup:

• chrony attempts to do time sync but fails because DNS isn't working

• DNS doesn't work because the robot doesn't have proper timekeeping

And so the robot is stuck in a weird state where it can be accessed via ssh on a local network and can ping IPs but can't do git pulls and such, so people may not even be aware that something's wrong.

Not sure if that's exactly the case or if there's another layer to this problem but doing a "nmcli con edit add google's dns" seems to always resolve it, so it would be good to have it as a stock fallback on every connection pifi makes internally.