feat: Improve Captain interactions, activity messages (#11493)

Show captain messages under the name of the assistant which generated
the message.

- Add support for `Captain::Assistant` sender type
- Add push_event_data for captain_assistants
- Add activity message handler for captain_assistants
- Update UI to show captain messages under the name of the assistant
- Fix the issue where openAI errors when image is sent
- Add support for custom name of the assistant

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

lib/integrations/slack/send_on_slack_service.rb

@@ -153,12 +153,12 @@ class Integrations::Slack::SendOnSlackService < Base::SendOnChannelService
   def sender_type(sender)
     if sender.instance_of?(Contact)
       'Contact'
-    elsif message.message_type == 'template' && sender.nil?
-      'Bot'
+    elsif sender.instance_of?(User)
+      'Agent'
     elsif message.message_type == 'activity' && sender.nil?
       'System'
     else
-      'Agent'
+      'Bot'
     end
   end