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__/users/delete-user.spec.ts

@@ -27,7 +27,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should delete a single user", async () => {
-        const user = await userModuleService.create({
+        const user = await userModuleService.createUsers({
           email: "member@test.com",
         })
 

integration-tests/modules/__tests__/users/list-users.spec.ts

@@ -27,7 +27,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should list users", async () => {
-        await userModuleService.create([
+        await userModuleService.createUsers([
           {
             email: "member@test.com",
           },

integration-tests/modules/__tests__/users/retrieve-user.spec.ts

@@ -27,7 +27,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should retrieve a single user", async () => {
-        const user = await userModuleService.create({
+        const user = await userModuleService.createUsers({
           email: "member@test.com",
         })
 

integration-tests/modules/__tests__/users/update-user.spec.ts

@@ -27,7 +27,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should update a single user", async () => {
-        const user = await userModuleService.create({
+        const user = await userModuleService.createUsers({
           email: "member@test.com",
         })