Enable push notifications feature for everyone and set notification mode to push

This commit hardcodes the push notification feature flag to true, in
preparation for purple testflight release.

It also changes the notification mode setting string, to ensure that we
won't have issues with people being stuck with local notification mode.

Testing
-------

Steps:
1. Run app
2. Ensure push notification flag is gone from developer Settings
3. Ensure notification mode is set to push, and that the push option is available
4. Ensure push notification settings appear as "synced successfully"

Conditions:
- iPhone 13 mini, iOS 17.6.1, on a device that was already under testing
- iPad simulator, iOS 17.5, brand new account

Changelog-Added: Push notification support
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damus/Models/PushNotificationClient.swift

@@ -18,7 +18,7 @@ struct PushNotificationClient {
     
     mutating func set_device_token(new_device_token: Data) async throws {
         self.device_token = new_device_token
-        if settings.enable_experimental_push_notifications && settings.notifications_mode == .push {
+        if settings.enable_push_notifications && settings.notification_mode == .push {
             try await self.send_token()
         }
     }