Integrate Notification Service into Tender Management System

- Added a new notification service to handle various notification types (email, SMS, push, OTP).
- Implemented configuration for the notification service, allowing customization via environment variables.
- Updated user and customer services to utilize the notification service for sending welcome emails and status updates.
- Introduced a builder pattern for constructing notification requests, enhancing usability and flexibility.
- Enhanced error handling and logging for notification operations, ensuring robust service integration.
- Updated documentation to include usage examples and configuration details for the new notification SDK.

pkg/notification/interfaces.go

@@ -0,0 +1,56 @@
+package notification
+
+import (
+	"context"
+)
+
+// NotificationService defines the interface for notification operations
+type NotificationService interface {
+	// SendNotification sends a notification using the configured client
+	SendNotification(ctx context.Context, req *NotificationRequest) (*NotificationResponse, error)
+
+	// SendEmail sends an email notification
+	SendEmail(ctx context.Context, email, message, userID string) (*NotificationResponse, error)
+
+	// SendSMS sends an SMS notification
+	SendSMS(ctx context.Context, phoneNumber, message, userID string) (*NotificationResponse, error)
+
+	// SendPush sends a push notification
+	SendPush(ctx context.Context, deviceToken, message, userID string) (*NotificationResponse, error)
+
+	// SendOTP sends an OTP notification
+	SendOTP(ctx context.Context, phoneNumber, message, userID string) (*NotificationResponse, error)
+
+	// Health checks if the notification service is available
+	Health(ctx context.Context) error
+}
+
+// Builder provides a fluent interface for building notification requests
+type Builder interface {
+	// SetEventType sets the event type
+	SetEventType(eventType EventType) Builder
+
+	// SetMessage sets the notification message
+	SetMessage(message string) Builder
+
+	// SetUserID sets the user ID
+	SetUserID(userID string) Builder
+
+	// SetEmail sets the email address
+	SetEmail(email string) Builder
+
+	// SetSMS sets the SMS phone number
+	SetSMS(phoneNumber string) Builder
+
+	// SetPush sets the push device token
+	SetPush(deviceToken string) Builder
+
+	// SetOTP sets the OTP phone number
+	SetOTP(phoneNumber string) Builder
+
+	// Build creates the notification request
+	Build() (*NotificationRequest, error)
+
+	// Send builds and sends the notification
+	Send(ctx context.Context) (*NotificationResponse, error)
+}