feat(electron): add offline mode (#8086)

fix AF-1334

It seems `session.enableNetworkEmulation({ offline: true });` does not work - https://github.com/electron/electron/issues/21250

implemented using an in-house solution.

When turned on:

![image.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/T2klNLEk0wxLh4NRDzhk/6805735b-1006-4e51-be46-c047b0f1a82c.png)

packages/common/infra/src/modules/feature-flag/constant.ts

@@ -96,6 +96,13 @@ export const AFFINE_FLAGS = {
     configurable: isCanaryBuild,
     defaultState: isCanaryBuild,
   },
+  enable_offline_mode: {
+    category: 'affine',
+    displayName: 'Offline Mode',
+    description: 'Enables offline mode.',
+    configurable: isDesktopEnvironment,
+    defaultState: false,
+  },
 } satisfies { [key in string]: FlagInfo };
 
 export type AFFINE_FLAGS = typeof AFFINE_FLAGS;