BASH-10 add local icon reference for squirrel

[csduarte]

To be able to customize icons, they can not be remote. Adding file:// to the beginning of the relative path will make it work locally.
"iconUrl": "file://resources/icon.ico"

• read and understood our Contributing Guidelines
• completed Mattermost Contributor Agreement
• executed npm run lint:js for proper code formatting

Test Cases
Replace resources/icon.ico file
Run npm run package:windows and make sure it runs properly and generates the files with the correct icon.

[yuya-oc]

The change is actually working. But please note that file is not accepted in electron-builder. https://www.electron.build/configuration/squirrel-windows