Chore/rm main entity concept (#7709)

**What**
Update the `MedusaService` class, factory and types to remove the concept of main modules. The idea being that all method will be explicitly named and suffixes to represent the object you are trying to manipulate.
This pr also includes various fixes in different modules

Co-authored-by: Stevche Radevski <4820812+sradevski@users.noreply.github.com>
Co-authored-by: Oli Juhl <59018053+olivermrbl@users.noreply.github.com>

integration-tests/modules/__tests__/link-modules/fulfillment-set-location.spec.ts

@@ -1,8 +1,7 @@
 import { ModuleRegistrationName, Modules } from "@medusajs/modules-sdk"
 import {
   IFulfillmentModuleService,
-  ISalesChannelModuleService,
-  IStockLocationServiceNext,
+  IStockLocationService,
 } from "@medusajs/types"
 import {
   ContainerRegistrationKeys,
@@ -20,8 +19,7 @@ medusaIntegrationTestRunner({
     describe("FulfillmentSet and Location", () => {
       let appContainer
       let fulfillmentModule: IFulfillmentModuleService
-      let locationModule: IStockLocationServiceNext
-      let scService: ISalesChannelModuleService
+      let locationModule: IStockLocationService
       let remoteQuery
       let remoteLink
 
@@ -33,7 +31,6 @@ medusaIntegrationTestRunner({
         locationModule = appContainer.resolve(
           ModuleRegistrationName.STOCK_LOCATION
         )
-        scService = appContainer.resolve(ModuleRegistrationName.SALES_CHANNEL)
         remoteQuery = appContainer.resolve(
           ContainerRegistrationKeys.REMOTE_QUERY
         )
@@ -41,12 +38,12 @@ medusaIntegrationTestRunner({
       })
 
       it("should query fulfillment set and location link with remote query", async () => {
-        const fulfillmentSet = await fulfillmentModule.create({
+        const fulfillmentSet = await fulfillmentModule.createFulfillmentSets({
           name: "Test fulfillment set",
           type: "delivery",
         })
 
-        const euWarehouse = await locationModule.create({
+        const euWarehouse = await locationModule.createStockLocations({
           name: "EU Warehouse",
         })