feat(medusa): Add ProductVariantInventoryService (#2883)

* add mw feature flag

* add services

* add types

* add module interfaces

* add interface export

* add models for mw

* to be ammended

* remove featureflag

* use correct count

* update cart completion strategy

* swap service conversion

* update return service

* update order service

* update claim service

* add exception to claim item

* update cart service

* add indicies

* add changeset

* nullable changes in store

* store model update

* fix unit tests

* remove old inventory service

* format integration test

* update snapshots

* remove old inventory service tests

* update snapshots

* remove old code

* option updates

* naming

* add jsdoc to pv inventory service

* rename class variables

* pr feedback

* rename option to context

* if(variant_id) instead of if(typeof varia...)

* update tests

* add jsdoc

* go for custom

* update code for readability

.changeset/wise-mangos-design.md

@@ -0,0 +1,8 @@
+---
+"@medusajs/medusa": patch
+---
+
+Add services: 
+- `sales-channel-inventory`
+- `sales-channel-location`
+- `product-variant-inventory`