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/medusa/src/api/admin/feature-flags/route.ts

@@ -1,7 +1,4 @@
-import {
-  MedusaRequest,
-  MedusaResponse,
-} from "@medusajs/framework/http"
+import { MedusaRequest, MedusaResponse } from "@medusajs/framework/http"
 import { ContainerRegistrationKeys } from "@medusajs/framework/utils"
 
 export const AUTHENTICATE = false
@@ -13,14 +10,14 @@ export const GET = async (
   const featureFlagRouter = req.scope.resolve(
     ContainerRegistrationKeys.FEATURE_FLAG_ROUTER
   ) as any
-  
+
   const flags = featureFlagRouter.listFlags()
-  
+
   // Convert array of flags to a simple key-value object
   const featureFlags: Record<string, boolean> = {}
-  flags.forEach(flag => {
+  flags.forEach((flag) => {
     featureFlags[flag.key] = flag.value
   })
-  
+
   res.json({ feature_flags: featureFlags })
-}
+}

packages/medusa/src/api/admin/products/middlewares.ts

@@ -1,10 +1,11 @@
 import {
-  featureFlagRouter,
   validateAndTransformBody,
   validateAndTransformQuery,
 } from "@medusajs/framework"
-import multer from "multer"
 import { maybeApplyLinkFilter, MiddlewareRoute } from "@medusajs/framework/http"
+import { FeatureFlag } from "@medusajs/framework/utils"
+import multer from "multer"
+import IndexEngineFeatureFlag from "../../../feature-flags/index-engine"
 import { DEFAULT_BATCH_ENDPOINTS_SIZE_LIMIT } from "../../../utils/middlewares"
 import { createBatchBody } from "../../utils/validators"
 import * as QueryConfig from "./query-config"
@@ -33,7 +34,6 @@ import {
   CreateProduct,
   CreateProductVariant,
 } from "./validators"
-import IndexEngineFeatureFlag from "../../../loaders/feature-flags/index-engine"
 
 const upload = multer({ storage: multer.memoryStorage() })
 
@@ -47,7 +47,7 @@ export const adminProductRoutesMiddlewares: MiddlewareRoute[] = [
         QueryConfig.listProductQueryConfig
       ),
       (req, res, next) => {
-        if (featureFlagRouter.isFeatureEnabled(IndexEngineFeatureFlag.key)) {
+        if (FeatureFlag.isFeatureEnabled(IndexEngineFeatureFlag.key)) {
           return next()
         }
 

packages/medusa/src/api/admin/products/route.ts

@@ -1,5 +1,4 @@
 import { createProductsWorkflow } from "@medusajs/core-flows"
-import { featureFlagRouter } from "@medusajs/framework"
 import {
   AuthenticatedMedusaRequest,
   MedusaResponse,
@@ -7,15 +6,19 @@ import {
   refetchEntity,
 } from "@medusajs/framework/http"
 import { AdditionalData, HttpTypes } from "@medusajs/framework/types"
-import { ContainerRegistrationKeys, isPresent } from "@medusajs/framework/utils"
-import IndexEngineFeatureFlag from "../../../loaders/feature-flags/index-engine"
+import {
+  ContainerRegistrationKeys,
+  FeatureFlag,
+  isPresent,
+} from "@medusajs/framework/utils"
+import IndexEngineFeatureFlag from "../../../feature-flags/index-engine"
 import { remapKeysForProduct, remapProductResponse } from "./helpers"
 
 export const GET = async (
   req: AuthenticatedMedusaRequest<HttpTypes.AdminProductListParams>,
   res: MedusaResponse<HttpTypes.AdminProductListResponse>
 ) => {
-  if (featureFlagRouter.isFeatureEnabled(IndexEngineFeatureFlag.key)) {
+  if (FeatureFlag.isFeatureEnabled(IndexEngineFeatureFlag.key)) {
     // Use regular list when no filters are provided
     // TODO: Tags and categories are not supported by the index engine yet
     if (

packages/medusa/src/api/admin/views/[entity]/configurations/middleware.ts

@@ -1,10 +1,10 @@
-import { 
-  MedusaRequest, 
-  MedusaResponse, 
-  MedusaNextFunction 
+import {
+  MedusaNextFunction,
+  MedusaRequest,
+  MedusaResponse,
 } from "@medusajs/framework/http"
 import { ContainerRegistrationKeys } from "@medusajs/framework/utils"
-import ViewConfigurationsFeatureFlag from "../../../../../loaders/feature-flags/view-configurations"
+import ViewConfigurationsFeatureFlag from "../../../../../feature-flags/view-configurations"
 
 export const ensureViewConfigurationsEnabled = async (
   req: MedusaRequest,
@@ -14,14 +14,14 @@ export const ensureViewConfigurationsEnabled = async (
   const flagRouter = req.scope.resolve(
     ContainerRegistrationKeys.FEATURE_FLAG_ROUTER
   ) as any
-  
+
   if (!flagRouter.isFeatureEnabled(ViewConfigurationsFeatureFlag.key)) {
     res.status(404).json({
       type: "not_found",
-      message: "Route not found"
+      message: "Route not found",
     })
     return
   }
-  
+
   next()
-}
+}