feat: add frontier endpoint to access billing account details (#409)

Author: rohilsurana

raystack/frontier/v1beta1/frontier.proto

@@ -1931,6 +1931,8 @@ message GetBillingAccountRequest {
 
   bool with_payment_methods = 3;
 
+  bool with_billing_details = 4;
+
   repeated string expand = 101;
 }
 
@@ -1940,6 +1942,9 @@ message GetBillingAccountResponse {
 
   // List of payment methods
   repeated PaymentMethod payment_methods = 2;
+
+  // Billing details
+  BillingAccountDetails billing_details = 3;
 }
 
 message UpdateBillingAccountRequest {

raystack/frontier/v1beta1/models.proto

@@ -605,6 +605,18 @@ message BillingAccount {
   Organization organization = 101 [(google.api.field_behavior) = OUTPUT_ONLY];
 }
 
+message BillingAccountDetails {
+  // credit_min is the minimum credit limit for the billing account
+  // default is 0, negative numbers work as overdraft, positive
+  // numbers work as minimum purchase limit
+  int64 credit_min = 1;
+
+  // due_in_days is the number of days after the invoice finalization
+  // that it will be considered overdue, if set to 0, the customer will
+  // be charged immediately
+  int64 due_in_days = 2;
+}
+
 message Subscription {
   reserved 9;