Add default body

[snikoletopoulos]

After importing a OpenAPI 3 swagger file, the request are almost ready to be used accept for the body.

It would be nice to have the json body parsed from the spec and left the values empty.
That way we wouldn't have to open the spec to look for the values that should be passed.

The spec can also provide examples, which can be used as a default value.

{
  "value": "",
  "optional_value": null,
  "value_with_default": "default"
}