Alerting: Persist AlertInstance ResolvedAt & LastSentAt (#89135)

* Alerting: Persist AlertInstance ResolvedAt & LastSentAt

* Fix test

* Modify existing tests

* Fix merge conflicts from nullable LastSentAt & ResolvedAt

pkg/services/sqlstore/migrations/migrations.go

@@ -123,6 +123,8 @@ func (oss *OSSMigrations) AddMigration(mg *Migrator) {
 	accesscontrol.AddManagedFolderAlertingSilencesActionsMigrator(mg)
 
 	ualert.AddRecordingRuleColumns(mg)
+
+	ualert.AddStateResolvedAtColumns(mg)
 }
 
 func addStarMigrations(mg *Migrator) {

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

@@ -0,0 +1,18 @@
+package ualert
+
+import "github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+
+// AddStateResolvedAtColumns adds columns to alert_instance to represent ResolvedAt and LastSentAt.
+func AddStateResolvedAtColumns(mg *migrator.Migrator) {
+	mg.AddMigration("add resolved_at column to alert_instance table", migrator.NewAddColumnMigration(migrator.Table{Name: "alert_instance"}, &migrator.Column{
+		Name:     "resolved_at",
+		Type:     migrator.DB_BigInt, // BigInt, to match existing time fields.
+		Nullable: true,
+	}))
+
+	mg.AddMigration("add last_sent_at column to alert_instance table", migrator.NewAddColumnMigration(migrator.Table{Name: "alert_instance"}, &migrator.Column{
+		Name:     "last_sent_at",
+		Type:     migrator.DB_BigInt,
+		Nullable: true,
+	}))
+}