Make BillingModule.OVERALL_INVOICE_PREFIX configurable

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=221700223

java/google/registry/config/RegistryConfig.java

@@ -692,6 +692,18 @@ public final class RegistryConfig {
       return ImmutableList.copyOf(config.billing.invoiceEmailRecipients);
     }
 
+    /**
+     * Returns the file prefix for the invoice CSV file.
+     *
+     * @see google.registry.beam.invoicing.InvoicingPipeline
+     * @see google.registry.reporting.billing.BillingEmailUtils
+     */
+    @Provides
+    @Config("invoiceFilePrefix")
+    public static String provideInvoiceFilePrefix(RegistryConfigSettings config) {
+      return config.billing.invoiceFilePrefix;
+    }
+
     /**
      * Returns the Google Cloud Storage bucket for staging escrow deposits pending upload.
      *