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>

packages/modules/notification/src/models/index.ts

@@ -1,2 +1,3 @@
-export { default as NotificationModel } from "./notification"
+export { default as Notification } from "./notification"
 export { default as NotificationProvider } from "./notification-provider"
+

packages/modules/notification/src/models/notification-provider.ts

@@ -9,7 +9,7 @@ import {
   PrimaryKey,
   Property,
 } from "@mikro-orm/core"
-import NotificationModel from "./notification"
+import Notification from "./notification"
 
 @Entity()
 export default class NotificationProvider {
@@ -29,10 +29,10 @@ export default class NotificationProvider {
   channels: string[]
 
   @OneToMany({
-    entity: () => NotificationModel,
+    entity: () => Notification,
     mappedBy: (notification) => notification.provider_id,
   })
-  notifications = new Collection<NotificationModel>(this)
+  notifications = new Collection<Notification>(this)
 
   @BeforeCreate()
   onCreate() {

packages/modules/notification/src/models/notification.ts

@@ -35,7 +35,7 @@ const NotificationReceiverIdIndex = createPsqlIndexStatementHelper({
 @NotificationReceiverIdIndex.MikroORMIndex()
 @Entity({ tableName: "notification" })
 // Since there is a native `Notification` type, we have to call this something else here and in a couple of other places.
-export default class NotificationModel {
+export default class Notification {
   @PrimaryKey({ columnType: "text" })
   id: string