feat: Remove Config::SentboxWatch (#7178)

The motivation is to reduce code complexity, get rid of the extra IMAP connection and cases when
messages are added to chats by Inbox and Sentbox loops in parallel which leads to various message
sorting bugs, particularly to outgoing messages breaking sorting of incoming ones which are fetched
later, but may have a smaller "Date".

src/scheduler/connectivity.rs

@@ -90,7 +90,7 @@ impl DetailedConnectivity {
             DetailedConnectivity::Preparing => Some(Connectivity::Working),
 
             // Just don't return a connectivity, probably the folder is configured not to be
-            // watched or there is e.g. no "Sent" folder, so we are not interested in it
+            // watched, so we are not interested in it.
             DetailedConnectivity::NotConfigured => None,
 
             DetailedConnectivity::Idle => Some(Connectivity::Connected),
@@ -378,7 +378,6 @@ impl Context {
         // Add e.g.
         //                              Incoming messages
         //                               - "Inbox": Connected
-        //                               - "Sent": Connected
         // =============================================================================================
 
         let watched_folders = get_watched_folder_configs(self).await?;