feat: scroll to bottom on new user message

when the user sends a new message, and if the user is at an older position
in the timeline, then neochat should automatically scroll to the latest message and mark all the messages as read

imports/NeoChat/Component/ChatBox/ChatBox.qml

@@ -16,6 +16,7 @@ Item {
     property alias inputFieldText: chatBar.inputFieldText
 
     signal fancyEffectsReasonFound(string fancyEffect)
+    signal messageSent()
 
     Kirigami.Theme.colorSet: Kirigami.Theme.View
 
@@ -150,6 +151,7 @@ Item {
         onMessageSent: {
             closeAll()
             checkForFancyEffectsReason()
+            root.messageSent();
         }
     }