Alerting: Remove internal labels from prometheus compatible API responses (#46548)

* Alerting: Remove internal labels from prometheus compatible API responses

* Appease the linter

* Fix integration tests

* Fix API documentation & linter

* move removal of internal labels to the models

pkg/services/ngalert/models/alert_rule.go

@@ -18,12 +18,9 @@ var (
 	// ErrAlertRuleFailedGenerateUniqueUID is an error for failure to generate alert rule UID
 	ErrAlertRuleFailedGenerateUniqueUID = errors.New("failed to generate alert rule UID")
 	// ErrCannotEditNamespace is an error returned if the user does not have permissions to edit the namespace
-	ErrCannotEditNamespace = errors.New("user does not have permissions to edit the namespace")
-	// ErrRuleGroupNamespaceNotFound
-	ErrRuleGroupNamespaceNotFound = errors.New("rule group not found under this namespace")
-	// ErrAlertRuleFailedValidation
-	ErrAlertRuleFailedValidation = errors.New("invalid alert rule")
-	// ErrAlertRuleUniqueConstraintViolation
+	ErrCannotEditNamespace                = errors.New("user does not have permissions to edit the namespace")
+	ErrRuleGroupNamespaceNotFound         = errors.New("rule group not found under this namespace")
+	ErrAlertRuleFailedValidation          = errors.New("invalid alert rule")
 	ErrAlertRuleUniqueConstraintViolation = errors.New("a conflicting alert rule is found: rule title under the same organisation and folder should be unique")
 )
 
@@ -77,6 +74,12 @@ const (
 	OkErrState       ExecutionErrorState = "OK"
 )
 
+// InternalLabelNameSet are labels that grafana automatically include as part of the labelset.
+var InternalLabelNameSet = map[string]struct{}{
+	RuleUIDLabel:      {},
+	NamespaceUIDLabel: {},
+}
+
 const (
 	RuleUIDLabel      = "__alert_rule_uid__"
 	NamespaceUIDLabel = "__alert_rule_namespace_uid__"
@@ -110,6 +113,29 @@ type AlertRule struct {
 	Labels      map[string]string
 }
 
+type LabelOption func(map[string]string)
+
+func WithoutInternalLabels() LabelOption {
+	return func(labels map[string]string) {
+		for k := range labels {
+			if _, ok := InternalLabelNameSet[k]; ok {
+				delete(labels, k)
+			}
+		}
+	}
+}
+
+// GetLabels returns the labels specified as part of the alert rule.
+func (alertRule *AlertRule) GetLabels(opts ...LabelOption) map[string]string {
+	labels := alertRule.Labels
+
+	for _, opt := range opts {
+		opt(labels)
+	}
+
+	return labels
+}
+
 // Diff calculates diff between two alert rules. Returns nil if two rules are equal. Otherwise, returns cmputil.DiffReport
 func (alertRule *AlertRule) Diff(rule *AlertRule, ignore ...string) cmputil.DiffReport {
 	var reporter cmputil.DiffReporter