nixos/networking: add hostname to `/etc/hosts` by default
nixos/networking: add hostname to `/etc/hosts` by default

We use `127.0.1.1` instead of `127.0.0.1` because some applications will fail if
`127.0.0.1` resolves to something other than `localhost`.

Debian does the same.

See #1248 and #36261.

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