Add AppImage support

[hojberg]

We should include support for AppImage in our builds (this was previously included with Tauri and lost in the migration to Electron)

[hojberg]

Possible package to use https://www.npmjs.com/package/electron-forge-maker-appimage

[J3RN]

I noticed that the v1.0.0 release was released as AppImage, but curiously v1.1.0 was not.

[hojberg]

@J3RN When we migrated from Tauri in the 1.0.0 release to Electron in the 1.1.0 release we accidentally missed adding the AppImage build configuration. This ticket is meant to track the work to restore that.