kdeconnect: Add sshfs as a dependency

[nixy]

Motivation for this change

kdeconnect depends on sshfs to mount the filesystem of android devices as discussed in #33442 and #27806

Things done

I've built this on a Linux server to test the build works, but haven't yet tested that kdeconnect works. I likely won't be able to finish testing this till Sunday night.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[nixy]

@FRidh
Tested this and it worked as expected. Should be good to merge if there aren't any objections.