docs: added middleware documentation (#3000)

* docs: added a middleware documentation

* docs: fixes based on eslint

docs/content/advanced/backend/price-selection-strategy/override.md

@@ -12,46 +12,51 @@ If you’re interested in learning what a price selection strategy is and how it
 
 Create a TypeScript or JavaScript file in `src/strategies` of your Medusa server project with a class that extends the `AbstractPriceSelectionStrategy` class:
 
-```typescript title=src/strategies/price.ts
-import { AbstractPriceSelectionStrategy, IPriceSelectionStrategy, PriceSelectionContext, PriceSelectionResult } from "@medusajs/medusa";
+```ts title=src/strategies/price.ts
+import { 
+  AbstractPriceSelectionStrategy, 
+  IPriceSelectionStrategy, 
+  PriceSelectionContext, 
+  PriceSelectionResult,
+} from "@medusajs/medusa"
 
-import { EntityManager } from "typeorm";
+import { EntityManager } from "typeorm"
 
-export default class MyPriceListStrategy extends AbstractPriceSelectionStrategy {
+export default class MyStrategy extends AbstractPriceSelectionStrategy {
 
   withTransaction(manager: EntityManager): IPriceSelectionStrategy {
     if (!manager) {
       return this
     }
 
-    return new MyPriceListStrategy()
+    return new MyStrategy()
   }
 
   async calculateVariantPrice(
     variant_id: string,
     context: PriceSelectionContext
   ): Promise<PriceSelectionResult> {
-    //TODO
+    // TODO
   }
 }
 ```
 
-You can use services or repositories in the strategy by adding them to the constructor and updating the parameters passed to the `MyPriceListStrategy` constructor in `withTransaction`. For example:
+You can use services or repositories in the strategy by adding them to the constructor and updating the parameters passed to the `MyStrategy` constructor in `withTransaction`. For example:
 
-```typescript
+```ts
 import { 
   AbstractPriceSelectionStrategy, 
   CustomerService, 
   IPriceSelectionStrategy, 
   PriceSelectionContext, 
-  PriceSelectionResult 
-} from "@medusajs/medusa";
+  PriceSelectionResult, 
+} from "@medusajs/medusa"
 
-export default class MyPriceListStrategy extends AbstractPriceSelectionStrategy {
+export default class MyStrategy extends AbstractPriceSelectionStrategy {
   private customerService: CustomerService
 
   constructor({
-    customerService
+    customerService,
   }) {
     super()
     this.customerService = customerService
@@ -62,11 +67,11 @@ export default class MyPriceListStrategy extends AbstractPriceSelectionStrategy
       return this
     }
 
-    return new MyPriceListStrategy({
-      customerService: this.customerService
+    return new MyStrategy({
+      customerService: this.customerService,
     })
   }
-  //...
+  // ...
 }
 ```
 
@@ -80,10 +85,10 @@ This method accepts the variant ID as a first parameter and the [context](./inde
 
 This method must return an object having the following fields:
 
-```typescript noReport
+```ts noReport
 {
-  originalPrice, //number | null
-  calculatedPrice, //number | null
+  originalPrice, // number | null
+  calculatedPrice, // number | null
   prices // MoneyAmount[]
 }
 ```