FR: resolv.conf for readonly / linked filesystems

### What are you trying to do?

Include tailscale in a better way in the raspberrymatic homecontrol system.
This system have /etc for example mounted read only and have a symlik to /var/... for the resolv.conf that is in a tmpfs an dynamically created.

I already found this PR: https://github.com/tailscale/tailscale/pull/8688 that discusses a similar issue.

### How should we solve this?

I would like to for example just provide via a "tailscale set" a different resolv.conf location or that you proper follow the symlink and just write the tmp and the real file into that folder.