Add support to disable chat join messages. Closes #1582 (#1743)

core/chat/server.go

@@ -91,7 +91,7 @@ func (s *Server) Addclient(conn *websocket.Conn, user *user.User, accessToken st
 	}
 
 	// Do not send user re-joined broadcast message if they've been active within 5 minutes.
-	shouldSendJoinedMessages := true
+	shouldSendJoinedMessages := data.GetChatJoinMessagesEnabled()
 	if previouslyLastSeen, ok := _lastSeenCache[user.ID]; ok && time.Since(previouslyLastSeen) < time.Minute*5 {
 		shouldSendJoinedMessages = false
 	}