feat: Support after param in messages end point (#6848)

Adds support to `after` param while fetching messages
Fixes: https://linear.app/chatwoot/issue/CW-1475/support-after-param-in-messages-end-point

app/finders/message_finder.rb

@@ -22,11 +22,29 @@ class MessageFinder
 
   def current_messages
     if @params[:after].present? && @params[:before].present?
-      messages.reorder('created_at asc').where('id >= ? AND id < ?', @params[:after].to_i, @params[:before].to_i).limit(1000)
+      messages_between(@params[:after].to_i, @params[:before].to_i)
     elsif @params[:before].present?
-      messages.reorder('created_at desc').where('id < ?', @params[:before].to_i).limit(20).reverse
+      messages_before(@params[:before].to_i)
+    elsif @params[:after].present?
+      messages_after(@params[:after].to_i)
     else
-      messages.reorder('created_at desc').limit(20).reverse
+      messages_latest
     end
   end
+
+  def messages_after(after_id)
+    messages.reorder('created_at asc').where('id > ?', after_id).limit(100)
+  end
+
+  def messages_before(before_id)
+    messages.reorder('created_at desc').where('id < ?', before_id).limit(20).reverse
+  end
+
+  def messages_between(after_id, before_id)
+    messages.reorder('created_at asc').where('id >= ? AND id < ?', after_id, before_id).limit(1000)
+  end
+
+  def messages_latest
+    messages.reorder('created_at desc').limit(20).reverse
+  end
 end