Fix asserts entries in JSON report

[jcamiel]

If I run the following tests:

hurl --test --json /tmp/run.json assert_json.hurl

Where assert_json.hurl is in the integration/test folder, the asserts entries in /tmp/run.json seem broken:

[
  {
    "filename": "assert_json.hurl",
    "entries": [
      {
        "request": {
          "method": "GET",
          "url": "http://localhost:8000/assert-json",
          "headers": [
            {
              "name": "Host",
              "value": "localhost:8000"
            },
            {
              "name": "Accept",
              "value": "*/*"
            },
            {
              "name": "User-Agent",
              "value": "hurl/1.3.1"
            }
          ],
          "cookies": [],
          "queryString": []
        },
        "response": {
          "httpVersion": "HTTP/1.0",
          "status": 200,
          "cookies": [],
          "headers": [
            {
              "name": "Content-Type",
              "value": "application/json"
            },
            {
              "name": "Content-Length",
              "value": "160"
            },
            {
              "name": "Server",
              "value": "Flask Server"
            },
            {
              "name": "Date",
              "value": "Sun, 10 Oct 2021 11:45:27 GMT"
            }
          ]
        },
        "captures": [],
        "asserts": [
          {
            "actual": "1.0",
            "expected": "1.0"
          },
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
          {},
...

The first assert entry :

         {
            "actual": "1.0",
            "expected": "1.0"
          },

has maybe not enough information. The assert result success of false is missing, and there is no information about the query, predicate etc...

In comparison, the hurl json export of this assert is:

{
           "query": {
              "type": "jsonpath",
              "expr": "$.count"
            },
            "predicate": {
              "type": "equal",
              "value": 5
            }
}

[fabricereix]

Simple json objects have been added for each assert in #301
such as

{
    "success": false,
    "message": "Assert Failure\n  --> tests/error_assert_value_error.hurl:4:0\n   |\n 4 | header \"content-type\" equals \"XXX\"\n   |   actual:   string <text/html; charset=utf-8>\n   |   expected: string <XXX>\n   |",
    "line": 4
}