feat: add trace_id for Read API

PiperOrigin-RevId: 429809867

google/cloud/bigquery/storage/v1/stream.proto

@@ -1,4 +1,4 @@
-// Copyright 2021 Google LLC
+// Copyright 2022 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -132,6 +132,14 @@ message ReadSession {
   // all streams are completely consumed. This estimate is based on
   // metadata from the table which might be incomplete or stale.
   int64 estimated_total_bytes_scanned = 12 [(google.api.field_behavior) = OUTPUT_ONLY];
+
+  // Optional. ID set by client to annotate a session identity.  This does not need
+  // to be strictly unique, but instead the same ID should be used to group
+  // logically connected sessions (e.g. All using the same ID for all sessions
+  // needed to complete a Spark SQL query is reasonable).
+  //
+  // Maximum length is 256 bytes.
+  string trace_id = 13 [(google.api.field_behavior) = OPTIONAL];
 }
 
 // Information about a single stream that gets data out of the storage system.