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/sales-channel-location.spec.ts

@@ -30,23 +30,23 @@ medusaIntegrationTestRunner({
       })
 
       it("should query carts, sales channels, customers, regions with remote query", async () => {
-        const scWebshop = await scService.create({
+        const scWebshop = await scService.createSalesChannels({
           name: "Webshop",
         })
 
-        const scCphStore = await scService.create({
+        const scCphStore = await scService.createSalesChannels({
           name: "CPH store",
         })
 
-        const scNycStore = await scService.create({
+        const scNycStore = await scService.createSalesChannels({
           name: "NYC store",
         })
 
-        const euWarehouse = await locationService.create({
+        const euWarehouse = await locationService.createStockLocations({
           name: "EU Warehouse",
         })
 
-        const usWarehouse = await locationService.create({
+        const usWarehouse = await locationService.createStockLocations({
           name: "US Warehouse",
         })