feat: add invoice-configs management functionality

internal/models/invoice_config_model.go

@@ -0,0 +1,14 @@
+package models
+
+import "time"
+
+type InvoiceConfig struct {
+	ID          int64     `json:"id"`
+	Name        string    `json:"name"`
+	Type        string    `json:"type"`
+	Description string    `json:"description"`
+	IsActive    bool      `json:"isActive"`
+	Metadata    []byte    `json:"metadata"`
+	CreatedAt   time.Time `json:"createdAt"`
+	UpdatedAt   time.Time `json:"updatedAt"`
+}