HtmlToImageConverterHttpPostFields Property
Returns the collection of HTTP POST fields to be used when accessing a web page in HTML to Image converter.
Each entry contains a parameter name and value. By default the converter
form-urlencodes the names and values when building the POST body; see
EncodeHttpPostFields if the values are already encoded.
If there are elements in collection then the converter will make a POST request to the web page URL
with the fields from this collection, otherwise it will make a GET request