chore(billing-platform): Add protos for set_pending_tax_transaction endpoint

proto/sentry_protos/billing/v1/services/contract/v1/endpoint_set_pending_tax_transaction.proto

@@ -0,0 +1,17 @@
+syntax = "proto3";
+
+package sentry_protos.billing.v1.services.contract.v1;
+
+// Records the tax provider's document reference on an invoice as a pending tax
+// transaction, linking the invoice to the opened tax document so it can be
+// committed or voided once the charge outcome is known.
+message SetPendingTaxTransactionRequest {
+  uint64 invoice_id = 1;
+  // The tax provider's reference for the opened (uncommitted) tax document.
+  string external_reference = 2;
+}
+
+message SetPendingTaxTransactionResponse {
+  // True if a matching invoice was found and updated.
+  bool updated = 1;
+}

rust/src/sentry_protos.billing.v1.services.contract.v1.rs

@@ -711,3 +711,20 @@ pub struct RolloverContractResponse {
     #[prost(uint64, tag = "3")]
     pub amount_billed: u64,
 }
+/// Records the tax provider's document reference on an invoice as a pending tax
+/// transaction, linking the invoice to the opened tax document so it can be
+/// committed or voided once the charge outcome is known.
+#[derive(Clone, PartialEq, Eq, Hash, ::prost::Message)]
+pub struct SetPendingTaxTransactionRequest {
+    #[prost(uint64, tag = "1")]
+    pub invoice_id: u64,
+    /// The tax provider's reference for the opened (uncommitted) tax document.
+    #[prost(string, tag = "2")]
+    pub external_reference: ::prost::alloc::string::String,
+}
+#[derive(Clone, Copy, PartialEq, Eq, Hash, ::prost::Message)]
+pub struct SetPendingTaxTransactionResponse {
+    /// True if a matching invoice was found and updated.
+    #[prost(bool, tag = "1")]
+    pub updated: bool,
+}