feat: added migrations

cmd/migrate/migrations/000001_create_orders_table.down.sql

@@ -0,0 +1 @@
+drop table if exists orders;

cmd/migrate/migrations/000001_create_orders_table.up.sql

@@ -0,0 +1,5 @@
+create table if not exists orders (
+    id uuid primary key,
+    item varchar(500) not null,
+    quantity integer not null check (quantity > 0)
+);