feat(metrics): Add util func to reset label allow lists

Adds a utility function `ResetLabelValueAllowLists` to reset the allow lists for label values.  This facilitates testing by allowing tests to clear the global state between runs and avoid unintended side effects.

staging/src/k8s.io/component-base/metrics/opts.go

@@ -37,6 +37,14 @@ var (
 	allowListLock        sync.RWMutex
 )
 
+// ResetLabelValueAllowLists resets the allow lists for label values.
+// NOTE: This should only be used in test.
+func ResetLabelValueAllowLists() {
+	allowListLock.Lock()
+	defer allowListLock.Unlock()
+	labelValueAllowLists = map[string]*MetricLabelAllowList{}
+}
+
 // KubeOpts is superset struct for prometheus.Opts. The prometheus Opts structure
 // is purposefully not embedded here because that would change struct initialization
 // in the manner which people are currently accustomed.

staging/src/k8s.io/component-base/metrics/opts_test.go

@@ -208,3 +208,21 @@ metric2,label2: v3`,
 		})
 	}
 }
+
+func TestResetLabelValueAllowLists(t *testing.T) {
+	labelValueAllowLists = map[string]*MetricLabelAllowList{
+		"metric1": {
+			labelToAllowList: map[string]sets.Set[string]{
+				"label1": sets.New[string]("v1", "v2"),
+			},
+		},
+		"metric2": {
+			labelToAllowList: map[string]sets.Set[string]{
+				"label2": sets.New[string]("v3"),
+			},
+		},
+	}
+
+	ResetLabelValueAllowLists()
+	assert.Empty(t, labelValueAllowLists)
+}