When `services.resolved.enable` is set to true, the file /etc/resolv.conf becomes a symlink to /etc/static/resolv.conf, which is a symlink to /run/systemd/resolve/stub-resolv.conf. Without this commit, tor does not have access to this file thanks to systemd confinement. This results in the following warning when tor starts:
```
[warn] Unable to stat resolver configuration in '/etc/resolv.conf': No such file or directory
[warn] Could not read your DNS config from '/etc/resolv.conf' - please investigate your DNS configuration. This is possibly a problem. Meanwhile, falling back to local DNS at 127.0.0.1.
```
To fix this, simply allow read-only access to the file when resolved is in use.
According to https://github.com/NixOS/nixpkgs/pull/161818#discussion_r824820462, the symlink may also point to /run/systemd/resolve/resolv.conf, so allow that as well.
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