feat: Add QR codes for WhatsApp, Messenger, and Telegram on inbox finish page (#12257)

Added QR code generation for multiple messaging platforms on the inbox
finish setup page. So users can scan QR codes to instantly test their
newly created channels.

**Supported Platforms**

  - **WhatsApp**: QR code for `https://wa.me/{phone_number}`
    - Supports both WhatsApp Cloud and Twilio WhatsApp inboxes
  - **Facebook Messenger**: QR code for `https://m.me/{page_id}`
    - All Facebook page inboxes
  - **Telegram**: QR code for `https://t.me/{bot_name}`
    - All Telegram bot inboxes

**How to test the changes**
You can test these changes by navigating to this URL
`{BASE_URL}/app/accounts/{account_id}/settings/inboxes/new/{inbox_id}/finish`
and simply replacing the inbox ID with one you've already created.

**Preview**

<img width="2432" height="1474" alt="CleanShot 2025-08-21 at 15 40
59@2x"
src="https://github.com/user-attachments/assets/4226133b-9793-48ca-bf79-903b7e003ef3"
/>

---------

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

app/views/api/v1/models/_inbox.json.jbuilder

@@ -115,6 +115,9 @@ end
 
 json.provider resource.channel.try(:provider)
 
+## Telegram Attributes
+json.bot_name resource.channel.try(:bot_name) if resource.telegram?
+
 ### WhatsApp Channel
 if resource.whatsapp?
   json.message_templates resource.channel.try(:message_templates)