feat(utils): define file config (#13283)

** What
 - Allow auto-loaded Medusa files to export a config object.
 - Currently supports isDisabled to control loading.
 - new instance `FeatureFlag` exported by `@medusajs/framework/utils`
 - `feature-flags` is now a supported folder for medusa projects, modules, providers and plugins. They will be loaded and added to `FeatureFlag`

** Why
 - Enables conditional loading of routes, migrations, jobs, subscribers, workflows, and other files based on feature flags.

```ts
// /src/feature-flags

import { FlagSettings } from "@medusajs/framework/feature-flags"

const CustomFeatureFlag: FlagSettings = {
  key: "custom_feature",
  default_val: false,
  env_key: "FF_MY_CUSTOM_FEATURE",
  description: "Enable xyz",
}

export default CustomFeatureFlag
```

```ts
// /src/modules/my-custom-module/migration/Migration20250822135845.ts

import { FeatureFlag } from "@medusajs/framework/utils"

export class Migration20250822135845 extends Migration {
  override async up(){ }
  override async down(){ }
}

defineFileConfig({
  isDisabled: () => !FeatureFlag.isFeatureEnabled("custom_feature")
})
```

packages/core/utils/src/dal/index.ts

@@ -1,10 +1,11 @@
+export * from "./mikro-orm/base-entity"
 export * from "./mikro-orm/big-number-field"
+export * from "./mikro-orm/custom-db-migrator"
+export * from "./mikro-orm/decorators/searchable"
 export * from "./mikro-orm/mikro-orm-create-connection"
 export * from "./mikro-orm/mikro-orm-free-text-search-filter"
 export * from "./mikro-orm/mikro-orm-repository"
-export * from "./mikro-orm/mikro-orm-soft-deletable-filter"
 export * from "./mikro-orm/mikro-orm-serializer"
-export * from "./mikro-orm/base-entity"
+export * from "./mikro-orm/mikro-orm-soft-deletable-filter"
 export * from "./mikro-orm/utils"
-export * from "./mikro-orm/decorators/searchable"
 export * from "./utils"

packages/core/utils/src/dal/mikro-orm/custom-db-migrator.ts

@@ -0,0 +1,59 @@
+import { Constructor } from "@medusajs/types"
+import { MikroORM, Utils } from "@mikro-orm/core"
+import {
+  Migrator as BaseMigrator,
+  Migration,
+  UmzugMigration,
+} from "@mikro-orm/migrations"
+import { isFileDisabled, isFileSkipped } from "../../common/define-file-config"
+import { dynamicImport } from "../../common/dynamic-import"
+
+export class CustomDBMigrator extends BaseMigrator {
+  static register(orm: MikroORM): void {
+    orm.config.registerExtension(
+      "@mikro-orm/migrator",
+      () => new CustomDBMigrator(orm.em as any)
+    )
+  }
+
+  resolve(params) {
+    require(params.path)
+    if (isFileDisabled(params.path)) {
+      return {
+        name: "Noop",
+        up: () => {},
+        down: () => {},
+      } as any
+    }
+
+    const $this = this as any
+    const createMigrationHandler = async (method) => {
+      const migration = await Utils.dynamicImport(params.path)
+      const MigrationClass = Object.values(
+        migration
+      )[0] as Constructor<Migration>
+      const instance = new MigrationClass($this.driver, $this.config)
+      await $this.runner.run(instance, method)
+    }
+
+    return {
+      name: $this.storage.getMigrationName(params.name),
+      up: () => createMigrationHandler("up"),
+      down: () => createMigrationHandler("down"),
+    }
+  }
+
+  async getPendingMigrations(): Promise<UmzugMigration[]> {
+    const pending = await super.getPendingMigrations()
+
+    // Filter out migrations that are disabled by file config
+    return pending.filter(async (pendingFile: UmzugMigration) => {
+      const migration = await dynamicImport(pendingFile.path!)
+      if (isFileSkipped(migration)) {
+        return false
+      }
+
+      return true
+    })
+  }
+}

packages/core/utils/src/dal/mikro-orm/mikro-orm-create-connection.ts

@@ -3,6 +3,7 @@ import { Filter as MikroORMFilter } from "@mikro-orm/core"
 import { TSMigrationGenerator } from "@mikro-orm/migrations"
 import { isString, retryExecution, stringifyCircular } from "../../common"
 import { normalizeMigrationSQL } from "../utils"
+import { CustomDBMigrator } from "./custom-db-migrator"
 
 type FilterDef = Parameters<typeof MikroORMFilter>[0]
 
@@ -107,6 +108,7 @@ export async function mikroOrmCreateConnection(
         false
       ),
     },
+    extensions: [CustomDBMigrator],
     // We don't want to do any DB checks when establishing the connection. This happens once when creating the pg_connection, and it can happen again explicitly if necessary.
     connect: false,
     ensureDatabase: false,