feat: Improve scrolling for last message on agent side (#2421)

* Improve chat widget scrolling

* refactor the class names to snake-case

* refactor the scrollTop calculations to a helper

* Add tests for scrollTopCalculationHelper

Co-authored-by: Nithin David Thomas <webofnithin@gmail.com>
Co-authored-by: Nithin David Thomas <1277421+nithindavid@users.noreply.github.com>

app/javascript/dashboard/components/widgets/conversation/helpers/scrollTopCalculationHelper.js

@@ -0,0 +1,18 @@
+const totalMessageHeight = (total, element) => {
+  return total + element.scrollHeight;
+};
+
+export const calculateScrollTop = (
+  conversationPanelHeight,
+  parentHeight,
+  relevantMessages
+) => {
+  // add up scrollHeight of a `relevantMessages`
+  let combinedMessageScrollHeight = [...relevantMessages].reduce(
+    totalMessageHeight,
+    0
+  );
+  return (
+    conversationPanelHeight - combinedMessageScrollHeight - parentHeight / 2
+  );
+};