feat(whatsapp): add webhook registration and status endpoints (#13551)

## Description

Adds webhook configuration management for WhatsApp Cloud API channels,
allowing administrators to check webhook status and register webhooks
directly from Chatwoot without accessing Meta Business Manager.

## Type of change

- [ ] New feature (non-breaking change which adds functionality)


## Screenshots

<img width="1130" height="676" alt="Screenshot 2026-03-05 at 7 04 18 PM"
src="https://github.com/user-attachments/assets/f5dcd9dd-8827-42c5-a52b-1024012703c2"
/>
<img width="1101" height="651" alt="Screenshot 2026-03-05 at 7 04 29 PM"
src="https://github.com/user-attachments/assets/e0bd59f9-2a90-4f24-87c0-b79f21e721ee"
/>



## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

config/routes.rb

@@ -218,6 +218,7 @@ Rails.application.routes.draw do
             delete :avatar, on: :member
             post :sync_templates, on: :member
             get :health, on: :member
+            post :register_webhook, on: :member
             if ChatwootApp.enterprise?
               resource :conference, only: %i[create destroy], controller: 'conference' do
                 get :token, on: :member