feat: process import from pre-processed chunks (#12527)

Fixes: FRMW-2968

In this PR we have done two major things.

- First, we remove storing CSV contents within the workflow storage and neither store the JSON payloads to be created/updated in workflows. Earlier, they all were workflow inputs, hence were stored in the workflow
- Introduce a naive concept of chunks and process chunks one by one. The next PR making chunking a bit more robust while using streams, adding ability to resume from the failed chunk and so on.

> [!IMPORTANT]  
> The new endpoint `/admin/product/imports` is not in use yet. But it will be after the next (final) PR.

## Old context in workflow storage

![CleanShot 2025-05-19 at 17 11 08@2x](https://github.com/user-attachments/assets/798bdcc9-a368-4c1f-afdd-2a77f5ce43e0)

## New context in workflow storage

![CleanShot 2025-05-19 at 17 15 08@2x](https://github.com/user-attachments/assets/0463d035-403f-4600-a9cd-5af24d5fee7c)

packages/medusa/src/api/admin/products/imports/[transaction_id]/confirm/route.ts

@@ -4,7 +4,7 @@ import {
 } from "@medusajs/framework/http"
 
 import {
-  importProductsWorkflowId,
+  importProductsAsChunksWorkflowId,
   waitConfirmationProductImportStepId,
 } from "@medusajs/core-flows"
 import { IWorkflowEngineService } from "@medusajs/framework/types"
@@ -28,7 +28,7 @@ export const POST = async (
       action: TransactionHandlerType.INVOKE,
       transactionId,
       stepId: waitConfirmationProductImportStepId,
-      workflowId: importProductsWorkflowId,
+      workflowId: importProductsAsChunksWorkflowId,
     },
     stepResponse: new StepResponse(true),
   })

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

@@ -2,10 +2,9 @@ import {
   MedusaResponse,
   AuthenticatedMedusaRequest,
 } from "@medusajs/framework/http"
-import { Modules } from "@medusajs/framework/utils"
 import type { HttpTypes } from "@medusajs/framework/types"
-import { importProductsWorkflow } from "@medusajs/core-flows"
 import type { AdminImportProductsType } from "../validators"
+import { importProductsAsChunksWorkflow } from "@medusajs/core-flows"
 
 /**
  * @version 2.8.0
@@ -14,13 +13,12 @@ export const POST = async (
   req: AuthenticatedMedusaRequest<AdminImportProductsType>,
   res: MedusaResponse<HttpTypes.AdminImportProductResponse>
 ) => {
-  const fileProvider = req.scope.resolve(Modules.FILE)
-  const file = await fileProvider.getAsBuffer(req.validatedBody.file_key)
-
-  const { result, transaction } = await importProductsWorkflow(req.scope).run({
+  const { result, transaction } = await importProductsAsChunksWorkflow(
+    req.scope
+  ).run({
     input: {
       filename: req.validatedBody.originalname,
-      fileContent: file.toString("utf-8"),
+      fileKey: req.validatedBody.file_key,
     },
   })