Use this to set the test cycle's custom fields.
The value should be a JSON object where the keys are the test cycle
custom field name and the values are the respective custom field
values.
Here's an example:
{
"single-choice": "option1",
"checkbox": true,
"userpicker": "5f8b5cf2ddfdcb0b8d1028bb",
"single-line": "a text line",
"datepicker": "2020-01-25",
"decimal": 10.55,
"number": 50,
"multi-choice": ["choice1","choice2"],
"multi-line": "first line<br />second line"
}
If there's a parsing error while parsing the JSON, the value will be
ignored and this field will then be empty upon page reload.