WireMock.Net: Loading mapping models with `JsonMatcher` is not working correctly

Describe the bug

Loading mapping models with JsonMatcher for Body matcher from a file is not working correctly.

Steps to reproduce:

1. Create mapping with JsonMatcher for the body and save it to file as follow

var requestBuilder = Request.Create()
	.WithPath("/api/v1.0/accounts/")
	.WithHeader("Content-Type", "application/json; charset=utf-8")
	.WithBody(new JsonMatcher(new { AccountIds = new[] { 1, 2, 3} }))
	.UsingPost();

var respondWithAProvider = wiremockServer.Given(requestBuilder, saveToFile: true);

var responseProvider = Response.Create()
	.WithStatusCode(200)
	.WithHeader("Content-Type", "application/json; charset=utf-8")
	.WithBody(JsonConvert.SerializeObject(new[] { 1, 2, 3 }));

wiremockServer.RespondWith(responseProvider);

1. As a result I get a file with the following content

{
  "Guid": "7d1c7dcc-eba1-4c3a-bc82-0a444fe9fcd9",
  "Request": {
    "Path": {
      "Matchers": [
        {
          "Name": "WildcardMatcher",
          "Pattern": "/api/v1.0/accounts/",
          "IgnoreCase": false
        }
      ]
    },
    "Methods": [
      "POST"
    ],
    "Headers": [
      {
        "Name": "Content-Type",
        "Matchers": [
          {
            "Name": "WildcardMatcher",
            "Pattern": "application/json; charset=utf-8",
            "IgnoreCase": true
          }
        ]
      }
    ],
    "Body": {
      "Matcher": {
        "Name": "JsonMatcher",
        "Pattern": {
          "AccountIds": [1, 2, 3]
        },
        "IgnoreCase": false
      }
    }
  },
  "Response": {
    "StatusCode": 200,
    "BodyDestination": "SameAsSource",
    "Body": "[1,2,3]",
    "Headers": {
      "Content-Type": "application/json; charset=utf-8"
    }
  }
}

1. Load mapping from file and feed it to the WireMock server

var content = File.ReadAllText(@"__admin\mappings\7d1c7dcc-eba1-4c3a-bc82-0a444fe9fcd9.json");
wiremockServer.WithMapping(content);

Expected behavior:

This is how requestBuilder looks like before saving mapping to a file

This is how requestBuilder looks like after loading from a file

The expectation is that the JsonMatcher works in the same way when loaded from a file and when created from the code. Currently, the pattern is always set to null when loading from a file.

Other notes

This is probably caused by this line where every pattern is cast to string (non-string values will result with a null) https://github.com/WireMock-Net/WireMock.Net/blob/7abf56eafaf9d57aff1234bf7c0ad0f408bb18d6/src/WireMock.Net/Serialization/MatcherMapper.cs#L39