fix(medusa,dashboard): don't send price updates for deleted regions/currencies (#9361)

**What**
- Fixes an issue where the admin dashboard would send region prices for deleted regions.
- Also, includes the implementation for `GET /admin/shipping-options/:id` and its corresponding SDK function.

**Why**
- When a region price for a deleted region was sent to the backend it would result in the insert hitting a not null constraint on the currency_code for prices. To avoid this the dashboard should not send region prices for deleted regions. 

**Additional context**
- Prices for deleted regions should ideally not be returned when fetching shipping option prices. However, we don't yet have a mechanism for cleaning up region prices after a region is deleted.

Fixes CC-540

packages/core/js-sdk/src/admin/shipping-option.ts

@@ -24,6 +24,21 @@ export class ShippingOption {
     )
   }
 
+  async retrieve(
+    id: string,
+    query?: HttpTypes.SelectParams,
+    headers?: ClientHeaders
+  ) {
+    return await this.client.fetch<HttpTypes.AdminShippingOptionResponse>(
+      `/admin/shipping-options/${id}`,
+      {
+        method: "GET",
+        headers,
+        query,
+      }
+    )
+  }
+
   async update(
     id: string,
     body: HttpTypes.AdminUpdateShippingOption,