Alerting: Persist alert instance FiredAt field (#105927)

* Persist alert instance fired at

* Update protos and tests

pkg/services/sqlstore/migrations/migrations.go

@@ -153,4 +153,6 @@ func (oss *OSSMigrations) AddMigration(mg *Migrator) {
 	accesscontrol.AddDatasourceDrilldownRemovalMigration(mg)
 
 	ualert.DropTitleUniqueIndexMigration(mg)
+
+	ualert.AddStateFiredAtColumn(mg)
 }

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

@@ -0,0 +1,12 @@
+package ualert
+
+import "github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+
+// AddStateFiredAtColumn adds a fired_at column to alert_instance to represent FiredAt.
+func AddStateFiredAtColumn(mg *migrator.Migrator) {
+	mg.AddMigration("add fired_at column to alert_instance table", migrator.NewAddColumnMigration(migrator.Table{Name: "alert_instance"}, &migrator.Column{
+		Name:     "fired_at",
+		Type:     migrator.DB_BigInt, // BigInt, to match existing time fields.
+		Nullable: true,
+	}))
+}