fix: exclude private and activity messages from public API (#7123)

- Exclude private messages

app/views/public/api/v1/models/_conversation.json.jbuilder

@@ -4,7 +4,7 @@ json.contact_last_seen_at resource.contact_last_seen_at.to_i
 json.status resource.status
 json.agent_last_seen_at resource.agent_last_seen_at.to_i
 json.messages do
-  json.array! resource.messages do |message|
+  json.array! resource.messages.chat do |message|
     json.partial! 'public/api/v1/models/message', formats: [:json], resource: message
   end
 end