* feat: Implement existing template linking for CSAT surveys
- Added functionality to link existing CSAT templates for WhatsApp channels.
- Introduced a new component for selecting existing templates.
- Updated the dashboard settings page to support template mode switching between creating new and using existing templates.
- Enhanced the CSAT template management service to handle linking existing templates and fetching available templates.
- Updated API routes to include linking and fetching available templates.
- Added tests for the new linking functionality and template availability checks.
* feat: Enhance CSAT template handling and validation across services and components
* feat: Refactor body variable extraction for CSAT templates and update related validations
* feat: Add linked_at field to CSAT template responses and update related handling
* feat: Add tests for ConversationDrop date formatting and CSAT template body variable handling
