Refactor Notification Management and Enhance Customer Features

- Updated the notification handling logic to utilize a new SDK for sending notifications, improving the flexibility and scalability of the notification system.
- Introduced new methods in the notification service for sending notifications to users and customers based on various target audience types, enhancing the notification delivery capabilities.
- Added a new endpoint to assign companies to a customer, improving customer management functionalities.
- Refactored the customer entity and forms to replace 'CompanyIDs' with 'Companies', ensuring consistency across the data model.
- Enhanced API documentation with Swagger comments for the new endpoint and updated notification structures, ensuring clarity for API consumers.

pkg/notification/entities.go

@@ -31,6 +31,7 @@ type NotificationRequest struct {
 	EventType   EventType           `json:"event_type" valid:"required,in(EMAIL|SMS|PUSH|OTP)"`
 	Priority    string              `json:"priority" valid:"required,in(low|medium|important)"`
 	ScheduledAt int64               `json:"scheduled_at"`
+	Metadata    map[string]any      `json:"metadata,omitempty" valid:"optional"`
 	Methods     NotificationMethods `json:"methods" valid:"required"`
 }