Add SqlClient using and TODO for generic repository

Added Microsoft.Data.SqlClient using directive to CatalogRepository.cs. Also added a TODO comment suggesting the use of a generic repository pattern to minimize code duplication.

DbFirst.Infrastructure/Repositories/CatalogRepository.cs

@@ -6,6 +6,7 @@ using System.Data;
 
 namespace DbFirst.Infrastructure.Repositories;
 
+// TODO: instead of creating implementation of repository per entity, consider using generic repository pattern (eg. IRepository<T>) to reduce code duplication.
 public class CatalogRepository : ICatalogRepository
 {
     private readonly ApplicationDbContext _db;