Allow HTTP probe steps to have names

To simplify debugging.

probes/http/http_probe.go

@@ -53,9 +53,13 @@ type httpProbe struct {
 func (p *httpProbe) RunProbe(ctx context.Context, debug *log.Logger) error {
 	browser := http.NewBrowser(p.tls, debug, p.dnsMap)
 	for idx, step := range p.script {
-		debug.Printf("sequence step #%d", idx+1)
+		stepName := fmt.Sprintf("#%d", idx+1)
+		if step.Name != "" {
+			stepName = fmt.Sprintf("%s - '%s'", stepName, step.Name)
+		}
+		debug.Printf("sequence step %s", stepName)
 		if err := http.CheckStep(ctx, browser, step, debug); err != nil {
-			err = fmt.Errorf("step #%d failed: %w", idx+1, err)
+			err = fmt.Errorf("step %s failed: %w", stepName, err)
 			debug.Printf("%v", err)
 			return err
 		}

protocol/http/step.go

@@ -17,6 +17,7 @@ type BasicAuth struct {
 // A Step in a script, a series of HTTP transactions whose results we can
 // verify somehow (right now just by needle-in-haystack string matching).
 type Step struct {
+	Name       string            `json:"name"`
 	Type       string            `json:"type"`
 	URL        string            `json:"url"`
 	Method     string            `json:"method"`