chore: Abstract module services (#6087)

**What**
Create a service abstraction for the modules internal service layer. The objective is to reduce the effort of building new modules when the logic is the same or otherwise allow to override the default behavior.

Co-authored-by: Oli Juhl <59018053+olivermrbl@users.noreply.github.com>

.changeset/twenty-emus-roll.md

@@ -0,0 +1,8 @@
+---
+"@medusajs/pricing": patch
+"@medusajs/product": patch
+"@medusajs/utils": patch
+"@medusajs/types": patch
+---
+
+chore: Abstract module services