Add batch number to customer invoice header

src/main.rs

@@ -224,6 +224,7 @@ struct IndexTemplate {
 #[template(path = "customer.html")]
 struct CustomerTemplate {
     customer: PreparedCustomer,
+    batch_number: String,
     period: String,
     generated_date: String,
 }
@@ -306,6 +307,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         let prepared = PreparedCustomer::from_customer(customer);
         let customer_html = CustomerTemplate {
             customer: prepared,
+            batch_number: batch_number.clone(),
             period: period.clone(),
             generated_date: generated_date.clone(),
         }