feat: Add currency module and remove currency models from region and pricing modules (#6536)

What:
- Creates a new currency module
- Removes currency model from the pricing module
- Removes currency model from region module

integration-tests/plugins/package.json

@@ -12,6 +12,7 @@
     "@medusajs/api-key": "workspace:^",
     "@medusajs/auth": "workspace:*",
     "@medusajs/cache-inmemory": "workspace:*",
+    "@medusajs/currency": "workspace:^",
     "@medusajs/customer": "workspace:^",
     "@medusajs/event-bus-local": "workspace:*",
     "@medusajs/inventory": "workspace:^",