feat(frontier): admins can list all billing accounts (#340)

Signed-off-by: Kush Sharma <[email protected]>

raystack/frontier/v1beta1/admin.proto

@@ -327,6 +327,15 @@ service AdminService {
       description: "Lists all the invoices from all the organizations in a Frontier instance. It can be filtered by organization.";
     };
   }
+
+  rpc ListAllBillingAccounts(ListAllBillingAccountsRequest) returns (ListAllBillingAccountsResponse) {
+    option (google.api.http) = {get: "/v1beta1/admin/billing/accounts"};
+    option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+      tags: "Billing";
+      summary: "List all billing accounts";
+      description: "Lists all the billing accounts from all the organizations in a Frontier instance. It can be filtered by organization.";
+    };
+  }
 }
 
 message ListAllUsersRequest {
@@ -560,4 +569,12 @@ message ListAllInvoicesRequest {
 
 message ListAllInvoicesResponse {
   repeated Invoice invoices = 1;
+}
+
+message ListAllBillingAccountsRequest {
+  string org_id = 1;
+}
+
+message ListAllBillingAccountsResponse {
+  repeated BillingAccount billing_accounts = 1;
 }