Allow mocking HTTP requests

Is your feature request related to a problem? Please describe. For an app I have, it needs to be able to generate previews of the content as a PNG. The data can easily be generated in an extension, but we need an easy way to send this data to the frontend (for both window mode and server mode)

Describe the solution you'd like It would be nice if extensions had a hook they could use for handling HTTP connections. General options such as the mocked Hostname could be added to the global neutralino config, and the extension would need some option to handle URLs, and return responses.

On server, this could be handled in the existing neutralino server. For window mode, all the Webview libraries have options for mocking HTTP calls.

Describe alternatives you've considered For sending image data, the only other option would be to serialize into something like Base64, then send as an event to the frontend, then the frontend can create a data URL to show it as an image. This could have memory issues depending on the size of the image, so it would be better to have a URL which show the image instead