feat: Add the basic implementation of notification module (#7282)

* feat: Add the basic implementation of notification module

* fix: Minor fixes and introduction of idempotency key

* fix: Changes based on PR review

packages/modules/notification/mikro-orm.config.dev.ts

@@ -0,0 +1,12 @@
+import * as entities from "./src/models"
+import { TSMigrationGenerator } from "@medusajs/utils"
+
+module.exports = {
+  entities: Object.values(entities),
+  schema: "public",
+  clientUrl: "postgres://postgres@localhost/medusa-notification",
+  type: "postgresql",
+  migrations: {
+    generator: TSMigrationGenerator,
+  },
+}