Cockpit should allow the user to specify a source for external widgets

[rafaellehmkuhl]

Today, we are fetching a JSON from BlueOS with information about the widgets (name, url, icon, etc), but with a little effort we could allow the user to specify another source (URL?) for that JSON so they can have external widgets without BlueOS.

[ES-Alexander]

Ideally this would also¹ support loading just a file from the filesystem, so you don't need a server to serve the file first.

Presumably that's quite easy with Electron (given we already make use of file-system access), but browser tabs do have a mechanism for uploading files, so that seems like at least one possible solution too.

Footnotes

1. I still think URL support would be valuable, because it's quite likely external extensions would be provided by a connected vehicle, instead of just from the device Cockpit's interface is running on. ↩