Rename web vital metrics

We're renaming them from webvital_xxx_xxx_xxx to browser_web_vital_xxx.
This change benefits us in three ways:
1. Browser metrics will be namespaced with browser_
2. webvital is two words, so web vital
3. We're assuming that users will have the context of web vital metrics
so that we can use the abbreviations which also helps with the display
of them at the end of the test run.

Closes: #884

examples/multiple-scenario.js

@@ -17,7 +17,7 @@ export const options = {
     },
   },
   thresholds: {
-    webvital_first_contentful_paint: ['max < 1000'],
+    browser_web_vital_fcp: ['max < 1000'],
     checks: ["rate==1.0"]
   }
 }

k6ext/metrics.go

@@ -24,12 +24,12 @@ type CustomMetrics struct {
 // VU Registry and returns our internal struct pointer.
 func RegisterCustomMetrics(registry *k6metrics.Registry) *CustomMetrics {
 	wvs := map[string]string{
-		webVitalFID:  "webvital_first_input_delay",
-		webVitalTTFB: "webvital_time_to_first_byte",
-		webVitalLCP:  "webvital_largest_content_paint",
-		webVitalCLS:  "webvital_cumulative_layout_shift",
-		webVitalINP:  "webvital_interaction_to_next_paint",
-		webVitalFCP:  "webvital_first_contentful_paint",
+		webVitalFID:  "browser_web_vital_fid",
+		webVitalTTFB: "browser_web_vital_ttfb",
+		webVitalLCP:  "browser_web_vital_lcp",
+		webVitalCLS:  "browser_web_vital_cls",
+		webVitalINP:  "browser_web_vital_inp",
+		webVitalFCP:  "browser_web_vital_fcp",
 	}
 	webVitals := make(map[string]*k6metrics.Metric)
 

tests/webvital_test.go

@@ -20,16 +20,16 @@ func TestWebVitalMetric(t *testing.T) {
 		browser  = newTestBrowser(t, withFileServer(), withSamplesListener(samples))
 		page     = browser.NewPage(nil)
 		expected = map[string]bool{
-			"webvital_time_to_first_byte":           false,
-			"webvital_time_to_first_byte_good":      false,
-			"webvital_first_contentful_paint":       false,
-			"webvital_first_contentful_paint_good":  false,
-			"webvital_largest_content_paint":        false,
-			"webvital_largest_content_paint_good":   false,
-			"webvital_first_input_delay":            false,
-			"webvital_first_input_delay_good":       false,
-			"webvital_cumulative_layout_shift":      false,
-			"webvital_cumulative_layout_shift_good": false,
+			"browser_web_vital_ttfb":      false,
+			"browser_web_vital_ttfb_good": false,
+			"browser_web_vital_fcp":       false,
+			"browser_web_vital_fcp_good":  false,
+			"browser_web_vital_lcp":       false,
+			"browser_web_vital_lcp_good":  false,
+			"browser_web_vital_fid":       false,
+			"browser_web_vital_fid_good":  false,
+			"browser_web_vital_cls":       false,
+			"browser_web_vital_cls_good":  false,
 		}
 	)