fix: ensure notification settings are cached from RPC

There are a bunch of notification related settings that cause RPC
calls when read from the UI in QML/Qt.

This is bad because whenever the view tries to read a notification
setting it causes an RPC call and then rerenders the view. This happens
pretty much every time a new signal arrives in the client.

To account for that we now fetch all notification settings once and mark
the service as initialized so it know when to simply return cached
values. The cache is updated when the notification settings change.

Fixes #10493

src/app_service/service/settings/dto/settings.nim

@@ -125,6 +125,17 @@ type
     gifRecents*: JsonNode
     gifFavorites*: JsonNode
     testNetworksEnabled*: bool
+    notificationsAllowNotifications*: bool
+    notificationsOneToOneChats*: string
+    notificationsGroupChats*: string
+    notificationsPersonalMentions*: string
+    notificationsGlobalMentions*: string
+    notificationsAllMessages*: string
+    notificationsContactRequests*: string
+    notificationsIdentityVerificationRequests*: string
+    notificationsSoundsEnabled*: bool
+    notificationsVolume*: int
+    notificationsMessagePreview*: int
 
 proc toPinnedMailserver*(jsonObj: JsonNode): PinnedMailserver =
   # we maintain pinned mailserver per fleet