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__/regions/admin/regions.spec.ts

@@ -87,9 +87,12 @@ medusaIntegrationTestRunner({
           deleted: true,
         })
 
-        const deletedRegion = await service.retrieve(updated.data.region.id, {
-          withDeleted: true,
-        })
+        const deletedRegion = await service.retrieveRegion(
+          updated.data.region.id,
+          {
+            withDeleted: true,
+          }
+        )
 
         // @ts-ignore
         expect(deletedRegion.deleted_at).toBeTruthy()
@@ -294,7 +297,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should throw on unknown properties in update", async () => {
-        const created = await service.create({
+        const created = await service.createRegions({
           name: "Test Region",
           currency_code: "usd",
         })
@@ -318,7 +321,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should get all regions and count", async () => {
-        await service.create([
+        await service.createRegions([
           {
             name: "Test",
             currency_code: "usd",
@@ -344,7 +347,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should support searching of regions", async () => {
-        await service.create([
+        await service.createRegions([
           {
             name: "APAC",
             currency_code: "usd",
@@ -369,7 +372,7 @@ medusaIntegrationTestRunner({
       })
 
       it("should get a region", async () => {
-        const [region] = await service.create([
+        const [region] = await service.createRegions([
           {
             name: "Test",
             currency_code: "usd",