Add async for saving backtests

src/Managing.Infrastructure.Database/PostgreSql/PostgreSqlBacktestRepository.cs

@@ -32,6 +32,16 @@ public class PostgreSqlBacktestRepository : IBacktestRepository
         _context.SaveChanges();
     }
 
+    public async Task InsertBacktestForUserAsync(User user, Backtest result)
+    {
+        ValidateBacktestData(result);
+        result.User = user;
+        
+        var entity = PostgreSqlMappers.Map(result);
+        _context.Backtests.Add(entity);
+        await _context.SaveChangesAsync();
+    }
+
     /// <summary>
     /// Validates that all numeric fields in the backtest are of the correct type
     /// </summary>