Migration for backfill of new launch plan column (#172)

The artifact trigger work previously prompted the decision to merge the notion of schedules and artifacts together into a launch plan trigger concept, a [new column](https://github.com/unionai/flyte/pull/83/files#diff-7189b1a0f8ed581ca15085037de7cd70b60305b90e42cc60f7eda13796577788R1227) for which was added to the launch plans table that would indicate whether the trigger type for a launch plan was a schedule or an artifact trigger.  This adds a backfill migration to admin.

Signed-off-by: Yee Hing Tong <wild-endeavor@users.noreply.github.com>

flyteadmin/pkg/repositories/config/migrations.go

@@ -1293,6 +1293,22 @@ var ContinuedMigrations = []*gormigrate.Migration{
 			return tx.Table("launch_plans").Migrator().DropColumn(&models.LaunchPlan{}, "launch_condition_type")
 		},
 	},
+	{
+		ID: "pg-continue-2024-03-backfill-launch-conditions",
+		Migrate: func(tx *gorm.DB) error {
+			query := `` +
+				`UPDATE launch_plans ` +
+				`SET launch_condition_type = 'SCHED' ` +
+				`WHERE schedule_type in ('CRON', 'RATE') ` +
+				`  AND launch_condition_type is null`
+			tx.Exec(query)
+
+			return tx.Error
+		},
+		Rollback: func(tx *gorm.DB) error {
+			return nil
+		},
+	},
 }
 
 var Migrations = append(LegacyMigrations, append(NoopMigrations, append(ContinuedMigrations, UnionMigrations...)...)...)