fix(ooniprobe): use ooniprobe-cli-unattended for unattended runs (#714)

This diff changes the software name used by unattended runs for which
we did not override the default software name (`ooniprobe-cli`).

It will become `ooniprobe-cli-unattended`. This software name is in line
with the one we use for Android, iOS, and desktop unattended runs.

While working in this diff, I introduced string constants for the run
types and a string constant for the default software name.

See https://github.com/ooni/probe/issues/2081.

internal/cmd/miniooni/libminiooni.go

@@ -412,7 +412,7 @@ func MainWithConfiguration(experimentName string, currentOptions Options) {
 
 	inputLoader := &engine.InputLoader{
 		CheckInConfig: &model.OOAPICheckInConfig{
-			RunType:  "manual",
+			RunType:  model.RunTypeManual,
 			OnWiFi:   true, // meaning: not on 4G
 			Charging: true,
 		},