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>

www/apps/resources/references/fulfillment/IFulfillmentModuleService/methods/fulfillment.IFulfillmentModuleService.create/page.mdx

@@ -17,7 +17,7 @@ This method creates fulfillment sets.
 ### Example
 
 ```ts
-const fulfillmentSets = await fulfillmentModuleService.create(
+const fulfillmentSets = await fulfillmentModuleService.createFulfillmentSets(
   [
     {
       name: "Shipping",
@@ -46,7 +46,7 @@ This method creates a fulfillment set.
 ### Example
 
 ```ts
-const fulfillmentSet = await fulfillmentModuleService.create({
+const fulfillmentSet = await fulfillmentModuleService.createFulfillmentSets({
   name: "Shipping",
   type: "default",
 })