Alerting: Support for simplified notification settings in rule API (#81011)

* Add notification settings to storage\domain and API models. Settings are a slice to workaround XORM mapping
* Support validation of notification settings when rules are updated

* Implement route generator for Alertmanager configuration. That fetches all notification settings.
* Update multi-tenant Alertmanager to run the generator before applying the configuration.

* Add notification settings labels to state calculation
* update the Multi-tenant Alertmanager to provide validation for notification settings

* update GET API so only admins can see auto-gen

pkg/services/sqlstore/migrations/migrations.go

@@ -117,6 +117,8 @@ func (oss *OSSMigrations) AddMigration(mg *Migrator) {
 	}
 
 	addKVStoreMySQLValueTypeLongTextMigration(mg)
+
+	ualert.AddRuleNotificationSettingsColumns(mg)
 }
 
 func addStarMigrations(mg *Migrator) {

pkg/services/sqlstore/migrations/ualert/rule_notification_settings_mig.go

@@ -0,0 +1,20 @@
+package ualert
+
+import (
+	"github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+)
+
+// AddRuleNotificationSettingsColumns creates a column for notification settings in the alert_rule and alert_rule_version tables.
+func AddRuleNotificationSettingsColumns(mg *migrator.Migrator) {
+	mg.AddMigration("add notification_settings column to alert_rule table", migrator.NewAddColumnMigration(migrator.Table{Name: "alert_rule"}, &migrator.Column{
+		Name:     "notification_settings",
+		Type:     migrator.DB_Text,
+		Nullable: true,
+	}))
+
+	mg.AddMigration("add notification_settings column to alert_rule_version table", migrator.NewAddColumnMigration(migrator.Table{Name: "alert_rule_version"}, &migrator.Column{
+		Name:     "notification_settings",
+		Type:     migrator.DB_Text,
+		Nullable: true,
+	}))
+}