feat: Add ConfigSynced event

Add an event for a case if a multi-device synced config value changed. Maybe the app needs to
refresh smth on such an event. For uniformity it is emitted on the source device too. The value is
omitted, otherwise it would be logged which might not be good for privacy.

src/events/payload.rs

@@ -4,6 +4,7 @@ use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
 
 use crate::chat::ChatId;
+use crate::config::Config;
 use crate::contact::ContactId;
 use crate::ephemeral::Timer as EphemeralTimer;
 use crate::message::MsgId;
@@ -261,8 +262,17 @@ pub enum EventType {
     ConnectivityChanged,
 
     /// The user's avatar changed.
+    /// Deprecated by `ConfigSynced`.
     SelfavatarChanged,
 
+    /// A multi-device synced config value changed. Maybe the app needs to refresh smth. For
+    /// uniformity this is emitted on the source device too. The value isn't here, otherwise it
+    /// would be logged which might not be good for privacy.
+    ConfigSynced {
+        /// Configuration key.
+        key: Config,
+    },
+
     /// Webxdc status update received.
     WebxdcStatusUpdate {
         /// Message ID.