Call update_device_chats automatically during configure (#1957)

update_device_chats() takes about 2 seconds on a modern device (Android) because the
welcome image file has to be written to the disk as a blob. The problem
was that this was done after the progress bar had vanished and before
anything else happened so that I thought that something had gone wrong
multiple times.

The UIs have to remove update_device_chats(), too..

src/config.rs

@@ -121,6 +121,8 @@ pub enum Config {
     #[strum(serialize = "sys.config_keys")]
     SysConfigKeys,
 
+    Bot,
+
     /// Whether we send a warning if the password is wrong (set to false when we send a warning
     /// because we do not want to send a second warning)
     #[strum(props(default = "0"))]