feat: Whatsapp embedded signup (#11612)

## Description

This PR introduces WhatsApp Embedded Signup functionality, enabling
users to connect their WhatsApp Business accounts through Meta's
streamlined OAuth flow without manual webhook configuration. This
significantly improves the user experience by automating the entire
setup process.

**Key Features:**

- Embedded signup flow using Facebook SDK and Meta's OAuth 2.0
- Automatic webhook registration and phone number configuration
- Enhanced provider selection UI with card-based design
- Real-time progress tracking during signup process
- Comprehensive error handling and user feedback


## Required Configuration

The following environment variables must be configured by administrators
before this feature can be used:
Super Admin Configuration (via
super_admin/app_config?config=whatsapp_embedded)

- `WHATSAPP_APP_ID`: The Facebook App ID for WhatsApp Business API
integration
- `WHATSAPP_CONFIGURATION_ID`: The Configuration ID for WhatsApp
Embedded Signup flow (obtained from Meta Developer Portal)
- `WHATSAPP_APP_SECRET`: The App Secret for WhatsApp Embedded Signup
flow (required for token exchange)
![Screenshot 2025-06-09 at 11 21
08 AM](https://github.com/user-attachments/assets/1615fb0d-27fc-4d9e-b193-9be7894ea93a)


## How Has This Been Tested?

#### Backend Tests (RSpec):

- Authentication validation for embedded signup endpoints
- Authorization code validation and error handling
- Missing business parameter validation
- Proper response format for configuration endpoint
- Unauthorized access prevention

#### Manual Test Cases:

- Complete embedded signup flow (happy path)
- Provider selection UI navigation
- Facebook authentication popup handling
- Error scenarios (cancelled auth, invalid business data, API failures)
- Configuration presence/absence behavior

## Related Screenshots:

![Screenshot 2025-06-09 at 7 48
18 PM](https://github.com/user-attachments/assets/34001425-df11-4d78-9424-334461e3178f)
![Screenshot 2025-06-09 at 7 48
22 PM](https://github.com/user-attachments/assets/c09f4964-3aba-4c39-9285-d1e8e37d0e33)
![Screenshot 2025-06-09 at 7 48
32 PM](https://github.com/user-attachments/assets/a34d5382-7a91-4e1c-906e-dc2d570c864a)
![Screenshot 2025-06-09 at 10 43
05 AM](https://github.com/user-attachments/assets/a15840d8-8223-4513-82e4-b08f23c95927)
![Screenshot 2025-06-09 at 10 42
56 AM](https://github.com/user-attachments/assets/8c345022-38b5-44c4-aba2-0cda81389c69)


Fixes
https://linear.app/chatwoot/issue/CW-2131/spec-for-whatsapp-cloud-channels-sign-in-with-facebook

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/controllers/super_admin/app_configs_controller.rb

@@ -39,8 +39,9 @@ class SuperAdmin::AppConfigsController < SuperAdmin::ApplicationController
       'email' => ['MAILER_INBOUND_EMAIL_DOMAIN'],
       'linear' => %w[LINEAR_CLIENT_ID LINEAR_CLIENT_SECRET],
       'slack' => %w[SLACK_CLIENT_ID SLACK_CLIENT_SECRET],
-      'notion' => %w[NOTION_CLIENT_ID NOTION_CLIENT_SECRET],
-      'instagram' => %w[INSTAGRAM_APP_ID INSTAGRAM_APP_SECRET INSTAGRAM_VERIFY_TOKEN INSTAGRAM_API_VERSION ENABLE_INSTAGRAM_CHANNEL_HUMAN_AGENT]
+      'instagram' => %w[INSTAGRAM_APP_ID INSTAGRAM_APP_SECRET INSTAGRAM_VERIFY_TOKEN INSTAGRAM_API_VERSION ENABLE_INSTAGRAM_CHANNEL_HUMAN_AGENT],
+      'whatsapp_embedded' => %w[WHATSAPP_APP_ID WHATSAPP_APP_SECRET WHATSAPP_CONFIGURATION_ID WHATSAPP_API_VERSION],
+      'notion' => %w[NOTION_CLIENT_ID NOTION_CLIENT_SECRET]
     }
 
     @allowed_configs = mapping.fetch(@config, %w[ENABLE_ACCOUNT_SIGNUP FIREBASE_PROJECT_ID FIREBASE_CREDENTIALS])