refactor: pass experiment arguments using a struct (#983)

Closes https://github.com/ooni/probe/issues/2358.

internal/engine/experiment/httphostheader/httphostheader.go

@@ -46,12 +46,10 @@ func (m *Measurer) ExperimentVersion() string {
 }
 
 // Run implements ExperimentMeasurer.Run.
-func (m *Measurer) Run(
-	ctx context.Context,
-	sess model.ExperimentSession,
-	measurement *model.Measurement,
-	callbacks model.ExperimentCallbacks,
-) error {
+func (m *Measurer) Run(ctx context.Context, args *model.ExperimentArgs) error {
+	_ = args.Callbacks
+	measurement := args.Measurement
+	sess := args.Session
 	if measurement.Input == "" {
 		return errors.New("experiment requires input")
 	}