build(electron): flatpak support for linux (#8439)

some issues
- app icon not showing correctly
- missing wayland support
- runtime is outdated

related to
- https://github.com/toeverything/AFFiNE/issues/3272
- https://github.com/toeverything/AFFiNE/issues/5985
- https://github.com/toeverything/AFFiNE/issues/6642

packages/frontend/apps/electron/package.json

@@ -34,6 +34,7 @@
     "@electron-forge/core-utils": "^7.3.0",
     "@electron-forge/maker-deb": "^7.5.0",
     "@electron-forge/maker-dmg": "^7.3.0",
+    "@electron-forge/maker-flatpak": "^7.5.0",
     "@electron-forge/maker-squirrel": "^7.3.0",
     "@electron-forge/maker-zip": "^7.3.0",
     "@electron-forge/plugin-auto-unpack-natives": "^7.3.0",