feat(miniooni): introduce the --repeat-every command line flag (#819)

Until OONI Run v2 has support for repeating the measurement with a schedule, introduce a command line flag requested by users to repeat a measurement every given number of seconds.

Part of ooni/probe#2184

internal/cmd/miniooni/libminiooni.go

@@ -45,6 +45,7 @@ type Options struct {
 	ProbeServicesURL string
 	Proxy            string
 	Random           bool
+	RepeatEvery      int64
 	ReportFile       string
 	TorArgs          []string
 	TorBinary        string
@@ -104,6 +105,10 @@ func init() {
 	getopt.FlagLong(
 		&globalOptions.Random, "random", 0, "Randomize inputs",
 	)
+	getopt.FlagLong(
+		&globalOptions.RepeatEvery, "repeat-every", 0,
+		"Repeat the measurement every INTERVAL number of seconds", "INTERVAL",
+	)
 	getopt.FlagLong(
 		&globalOptions.ReportFile, "reportfile", 'o',
 		"Set the report file path", "PATH",
@@ -283,7 +288,20 @@ func MainWithConfiguration(experimentName string, currentOptions Options) {
 		currentOptions.ReportFile = "report.jsonl"
 	}
 	log.Log = logger
+	for {
+		mainSingleIteration(logger, experimentName, currentOptions)
+		if currentOptions.RepeatEvery <= 0 {
+			break
+		}
+		log.Infof("waiting %ds before repeating the measurement", currentOptions.RepeatEvery)
+		log.Info("use Ctrl-C to interrupt miniooni")
+		time.Sleep(time.Duration(currentOptions.RepeatEvery) * time.Second)
+	}
+}
 
+// mainSingleIteration runs a single iteration. There may be multiple iterations
+// when the user specifies the --repeat-every command line flag.
+func mainSingleIteration(logger model.Logger, experimentName string, currentOptions Options) {
 	extraOptions := mustMakeMapAny(currentOptions.ExtraOptions)
 	annotations := mustMakeMapString(currentOptions.Annotations)