code: public final ListCollectionIdsPagedResponse listCollectionIds(String parent) {
      ListCollectionIdsRequest request =
          ListCollectionIdsRequest.newBuilder().setParent(parent).build();
      return listCollectionIds(request);
    }
docs: Lists all the collection IDs underneath a document.
  
  <p>Sample code:
  
  <pre><code>
  try (FirestoreClient firestoreClient = FirestoreClient.create()) {
  String formattedParent = AnyPathName.format("[PROJECT]", "[DATABASE]", "[DOCUMENT]", "[ANY_PATH]");
  for (String element : firestoreClient.listCollectionIds(formattedParent).iterateAll()) {
  // doThingsWith(element);
  }
  }
  </code></pre>
  
  @param parent The parent document. In the format:
  `projects/{project_id}/databases/{database_id}/documents/{document_path}`. For example:
  `projects/my-project/databases/my-database/documents/chatrooms/my-chatroom`
  @throws com.google.api.gax.rpc.ApiException if the remote call fails