added database connection string

api/appsettings.json

@@ -5,5 +5,8 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+  "ConnectionStrings": {
+    "DefaultConnection": "Host=localhost;Port=5432;Database=PersonsExercise;Username=postgres;Password=postgres"
+  }
 }