docs: Add upgrade guide for 1.16.0 (#5051)

* docs: Add upgrade guide for 1.16.0

* Update www/docs/content/upgrade-guides/medusa-core/1-16-0.md

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

* Update www/docs/content/upgrade-guides/medusa-core/1-16-0.md

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

---------

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

www/docs/content/upgrade-guides/medusa-core/1-16-0.md

@@ -0,0 +1,55 @@
+---
+description: 'Actions Required for v.1.16.0'
+sidebar_custom_props:
+  iconName: 'server-stack-solid'
+---
+
+# v1.16.0
+
+Version 1.16.0 of Medusa introduces breaking changes to database schemas.
+
+## Overview
+
+This release contains a migration that changes the relationship between the `MoneyAmount` and `ProductVariant` entities from Many-to-One to Many-to-Many.
+
+Additionally, the following foreign key constraints have been dropped:
+
+:::note
+
+These changes are only relevant if you are using the feature flag `isolate_product_domain`. Please be careful about enabling this flag, as it will introduce experimental and work-in-progress changes.
+
+:::
+
+- `ProductTaxRate` to `Product`
+- `ProductTypeTaxRate` to `ProductType`
+- `ClaimItem` to `ProductVariant`
+- `DiscountConditionProduct` to `Product`
+- `DiscountConditionProductCollection` to `ProductCollection`
+- `DiscountConditionProductTag` to `ProductTag`
+- `DiscountConditionProductType` to `ProductType`
+- `DiscountRule` to `Product`
+
+---
+
+## How to Update
+
+Run the following command in your project:
+
+```bash npm2yarn
+npm install @medusajs/medusa@1.16.0
+```
+
+To avoid unexpected issues with dependencies, it is also recommended to update all other Medusa plugins or packages you have installed. 
+
+---
+
+## Actions Required
+
+### Run Migrations
+
+After updating your Medusa server and before running it, run the following command to run the latest migrations:
+
+```bash
+npx medusa migrations run
+```
+