feat: add custom datetime format for Cloud Storage subscriptions

PiperOrigin-RevId: 619178723

google/pubsub/v1/pubsub.proto

@@ -203,7 +203,7 @@ message IngestionDataSourceSettings {
       KINESIS_PERMISSION_DENIED = 2;
 
       // Permission denied encountered while publishing to the topic. This can
-      // happen due to Pub/Sub SA has not been granted the [appropriate publish
+      // happen if the Pub/Sub SA has not been granted the [appropriate publish
       // permissions](https://cloud.google.com/pubsub/docs/access-control#pubsub.publisher)
       PUBLISH_PERMISSION_DENIED = 3;
 
@@ -1197,6 +1197,11 @@ message CloudStorageConfig {
   // Must not end in "/".
   string filename_suffix = 3 [(google.api.field_behavior) = OPTIONAL];
 
+  // Optional. User-provided format string specifying how to represent datetimes
+  // in Cloud Storage filenames. See the [datetime format
+  // guidance](https://cloud.google.com/pubsub/docs/create-cloudstorage-subscription#file_names).
+  string filename_datetime_format = 10 [(google.api.field_behavior) = OPTIONAL];
+
   // Defaults to text format.
   oneof output_format {
     // Optional. If set, message data will be written to Cloud Storage in text