feat(ooniprobe): add torsf to experimental group (#670)

Reference issue: https://github.com/ooni/probe/issues/1917.

I needed to change the summary key type returned by `torsf` to be a value. It seems the DB layer assumes that. If we pass it a pointer, it panics because it's experiment a value rather than a pointer 🤷.

cmd/ooniprobe/internal/nettests/groups.go

@@ -55,6 +55,7 @@ var All = map[string]Group{
 		Nettests: []Nettest{
 			DNSCheck{},
 			STUNReachability{},
+			TorSf{},
 		},
 	},
 }