Option to add Icon from local folder instead of URL

**Is your feature request related to a problem? Please describe.**
Our icons on our web-app are being dynamically created and therefore on each new release, the filename of the icon changed.
Since we're automating the creating of the twa-manifest it requires us to fetch our web manifest from production and prase the icon from the manifest.

**Describe the solution you'd like**
As a User, I would like to be able to add an icon from local folder instead of url.