CloudMigrations: Add config for alert rules state behavior and remove experimental feature toggle on alerts migration (#97254)

* CloudMigrations: add config for controlling alert rules state behavior

* CloudMigrations: remove experimental 'onPremToCloudMigrationsAlerts' feature toggle

pkg/setting/setting_cloud_migration.go

@@ -5,6 +5,14 @@ import (
 	"time"
 )
 
+const (
+	// GMSAlertRulesPaused configures Alert Rules to all be in Paused state.
+	GMSAlertRulesPaused = "paused"
+
+	// GMSAlertRulesUnchanged will not change the Alert Rules' states.
+	GMSAlertRulesUnchanged = "unchanged"
+)
+
 type CloudMigrationSettings struct {
 	IsTarget                    bool
 	GcomAPIToken                string
@@ -26,6 +34,7 @@ type CloudMigrationSettings struct {
 	TokenExpiresAfter           time.Duration
 	FeedbackURL                 string
 	FrontendPollInterval        time.Duration
+	AlertRulesState             string
 
 	IsDeveloperMode bool
 }
@@ -53,6 +62,7 @@ func (cfg *Cfg) readCloudMigrationSettings() {
 	cfg.CloudMigration.IsDeveloperMode = cloudMigration.Key("developer_mode").MustBool(false)
 	cfg.CloudMigration.FeedbackURL = cloudMigration.Key("feedback_url").MustString("")
 	cfg.CloudMigration.FrontendPollInterval = cloudMigration.Key("frontend_poll_interval").MustDuration(2 * time.Second)
+	cfg.CloudMigration.AlertRulesState = cloudMigration.Key("alert_rules_state").In(GMSAlertRulesPaused, []string{GMSAlertRulesPaused, GMSAlertRulesUnchanged})
 
 	if cfg.CloudMigration.SnapshotFolder == "" {
 		cfg.CloudMigration.SnapshotFolder = filepath.Join(cfg.DataPath, "cloud_migration")