Add newsletter subscription data to Excel export

[aniket-sainii]

This pull request adds the functionality to include the newsletter subscription status for each store in the Excel export of customer data. It ensures that for each store, the customer's subscription status is dynamically included in the export based on the existing logic in the system.

Changes:

1. Fetches all stores:
   • The stores are fetched using the ( _storeService.GetAllStoresAsync ) method.
2. Dynamically fetches subscription data:
   • The customer's subscription status is fetched for each store using the
     ( _newsLetterSubscriptionService.GetNewsLetterSubscriptionByEmailAndStoreIdAsync) method.
   • The subscription status is then displayed as a column for each store in the Excel export.

Attached File:
Customers Excel report.xlsx
A sample Excel export file is attached for your reference, showing the newly added subscription status column for each store.