feat: move create inventory to @medusajs/workflows (#5301)

**Why**
- We have some workflow-like flows in @medusajs/medusa. These should be moved over to the workflows package.
- Inventory Items <> Variant currently assume a 1-1 mapping. There should be support for a many-to-many mapping.

**What**
- PR introduces a feature flag for supporting many-to-many mappings for inventory and variants.
- Deletes legacy transaction handler in @medusajs/medusa.
- Adjusts existing createInventoryItems handler to remove dependency on variant data.

**Unkowns**
~~1. Couldn't find an existing test for the CreateProduct workflow. It should be tested that this still works as expected.~~
2. Have removed transaction managers as we should move to handling consistency through orchestration tooling. Are we ready for that?

.changeset/tame-queens-cough.md

@@ -0,0 +1,8 @@
+---
+"@medusajs/medusa": patch
+"@medusajs/inventory": patch
+"@medusajs/types": patch
+"@medusajs/utils": patch
+"@medusajs/workflows": patch
+---
+fix: move create inventory workflow to @medusajs/workflows