docs: Add 1.12.0 upgrade guide (#4204)

* docs: Add 1.12.0 upgrade guide

* Add note on breaking changes

* added new action required

* eslint fixes

* Add another breaking change note

---------

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

docs/content/upgrade-guides/medusa-core/1-12-0.md

@@ -0,0 +1,100 @@
+---
+description: 'Actions Required for v.1.12.0'
+sidebar_custom_props:
+  iconName: 'server-stack-solid'
+---
+
+# v1.12.0
+
+Version 1.12.0 of Medusa comes with database changes that require you run the migrations command and a minor breaking change to the `PriceSelectionStrategy`.
+
+## Overview
+
+This release contains migrations that introduce a range of new database indexes that will improve performance of your setup.
+
+Additionally, it brings minor breaking changes to the `PriceSelectionStrategy`. The method `calculateVariantPrice` now supports bulk calculating variant prices.
+
+Specifically, the following signature has changed:
+
+```ts
+// Before
+class MyStrategy extends 
+  AbstractPriceSelectionStrategy {
+  // ...
+  calculateVariantPrice(
+    variantId: string,
+    context: PriceSelectionContext
+  ): Promise<PriceSelectionResult> {
+    // ...
+  }
+}
+```
+
+```ts
+// Now
+class MyStrategy extends 
+  AbstractPriceSelectionStrategy {
+  // ...
+  calculateVariantPrice(data: {
+    variantId: string; 
+    quantity?: number;
+   }[],
+   context: PriceSelectionContext
+  ): Promise<Map<string, PriceSelectionResult>> {
+    // ...
+  }
+}
+```
+
+Finally, a clean up of our `@medusajs/utils` have also led to potential breaking changes. The clean-up resulted in the following:
+
+- The packages `class-validator` and `class-transformer` have been removed from `@medusajs/utils`.
+
+- The `TransactionBaseService` has been removed from `@medusajs/utils`. This class should be imported from `@medusajs/medusa`.
+
+- The utilities `build-query`, `db-aware-column`, `base-entity`, and `soft-deletable-entity` have been removed from `@medusajs/medusa`. These should be imported from @medusajs/medusa.
+
+---
+
+## How to Update
+
+Run the following command in the root directory of your Medusa Backend:
+
+```bash npm2yarn
+npm install @medusajs/medusa@1.12.0
+```
+
+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 @medusajs/medusa-cli migrations run
+```
+
+### Change PriceSelectionStrategy method
+
+If you've created a custom price selection strategy, or have using the `PriceSelectionStrategy`'s `calculateVariantPrice` method in your custom code, make sure to update its definition or usage based on the new signature:
+
+```ts
+class MyStrategy extends 
+  AbstractPriceSelectionStrategy {
+  // ...
+  calculateVariantPrice(data: {
+    variantId: string; 
+    quantity?: number;
+   }[],
+   context: PriceSelectionContext
+  ): Promise<Map<string, PriceSelectionResult>> {
+    // ...
+  }
+}
+```
+
+You can learn more in the [Price Selection Strategy](../../modules/price-lists/price-selection-strategy.md#calculatevariantprice-method) documentation.