Changed JsonSerialize to JsonConvert

MockContainer/MockContainer.cs

 using System.Text.Encodings.Web;
 using System.Text.Json;
-using System.Text.Json.Serialization;
+using Newtonsoft.Json;
 using Autofac;
 using FitConnect.Encryption;
 using FitConnect.Models.Api.Metadata;
@@ -135,10 +135,9 @@ public static class Container {
                 (string id, SubmitSubmissionDto dto) => {
                     Console.WriteLine(
                         $@"Submitting submission {id} with 
-                            {JsonSerializer.Serialize(dto, new JsonSerializerOptions {
-                                DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
-                                WriteIndented = true,
-                                Encoder = JavaScriptEncoder.Default
+                            {JsonConvert.SerializeObject(dto, new JsonSerializerSettings() {
+                                NullValueHandling = NullValueHandling.Ignore,
+                                Formatting = Formatting.Indented
                             })}");
                     return Task.Run(() => new SubmissionReducedDto());
                 });