feat(region): Add admin region get + list endpoints (#6322)

**What**
Add `GET /admin/regions`
Add `GET /admin/regions/:id`

Blocked by #6320 

Co-authored-by: Adrien de Peretti <25098370+adrien2p@users.noreply.github.com>

integration-tests/plugins/package.json

@@ -19,6 +19,7 @@
     "@medusajs/pricing": "workspace:^",
     "@medusajs/product": "workspace:^",
     "@medusajs/promotion": "workspace:^",
+    "@medusajs/region": "workspace:^",
     "@medusajs/utils": "workspace:^",
     "faker": "^5.5.3",
     "medusa-fulfillment-webshipper": "workspace:*",