Alerting: Add config disabled_labels to disable reserved labels (#51832)

* Alerting: Add config disabled_labels to disable reserved labels

[unified_alerting.reserved_labels]
disabled_labels

* Replace IsGrafanaFolderDisabled with more generic IsReservedLabelDisabled

* Simplify SchedulerCfg by including UnifiedAlertingSettings

pkg/setting/setting_unified_alerting.go

@@ -82,6 +82,7 @@ type UnifiedAlertingSettings struct {
 	// DefaultRuleEvaluationInterval default interval between evaluations of a rule.
 	DefaultRuleEvaluationInterval time.Duration
 	Screenshots                   UnifiedAlertingScreenshotSettings
+	ReservedLabels                UnifiedAlertingReservedLabelSettings
 }
 
 type UnifiedAlertingScreenshotSettings struct {
@@ -90,12 +91,22 @@ type UnifiedAlertingScreenshotSettings struct {
 	UploadExternalImageStorage bool
 }
 
+type UnifiedAlertingReservedLabelSettings struct {
+	DisabledLabels map[string]struct{}
+}
+
 // IsEnabled returns true if UnifiedAlertingSettings.Enabled is either nil or true.
 // It hides the implementation details of the Enabled and simplifies its usage.
 func (u *UnifiedAlertingSettings) IsEnabled() bool {
 	return u.Enabled == nil || *u.Enabled
 }
 
+// IsReservedLabelDisabled returns true if UnifiedAlertingReservedLabelSettings.DisabledLabels contains the given reserved label.
+func (u *UnifiedAlertingReservedLabelSettings) IsReservedLabelDisabled(label string) bool {
+	_, ok := u.DisabledLabels[label]
+	return ok
+}
+
 // readUnifiedAlertingEnabledSettings reads the settings for unified alerting.
 // It returns a non-nil bool and a nil error when unified alerting is enabled either
 // because it has been enabled in the settings or by default. It returns nil and
@@ -274,6 +285,15 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 	uaCfgScreenshots.UploadExternalImageStorage = screenshots.Key("upload_external_image_storage").MustBool(screenshotsDefaultUploadImageStorage)
 	uaCfg.Screenshots = uaCfgScreenshots
 
+	reservedLabels := iniFile.Section("unified_alerting.reserved_labels")
+	uaCfgReservedLabels := UnifiedAlertingReservedLabelSettings{
+		DisabledLabels: make(map[string]struct{}),
+	}
+	for _, label := range util.SplitString(reservedLabels.Key("disabled_labels").MustString("")) {
+		uaCfgReservedLabels.DisabledLabels[label] = struct{}{}
+	}
+	uaCfg.ReservedLabels = uaCfgReservedLabels
+
 	cfg.UnifiedAlerting = uaCfg
 	return nil
 }