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/medusa/src/subscribers/configurable-notifications.ts

@@ -69,7 +69,7 @@ export default async function configurableNotifications({
 
       // We don't want to fail all handlers, so we catch and log errors only
       try {
-        await notificationService.create(notificationData)
+        await notificationService.createNotifications(notificationData)
       } catch (err) {
         logger.error(
           `Failed to send notification for ${eventName}`,