code: public final BeginTransactionResponse beginTransaction(String database) {
  
      BeginTransactionRequest request =
          BeginTransactionRequest.newBuilder().setDatabase(database).build();
      return beginTransaction(request);
    }
docs: Starts a new transaction.
  
  <p>Sample code:
  
  <pre><code>
  try (FirestoreClient firestoreClient = FirestoreClient.create()) {
  String formattedDatabase = DatabaseRootName.format("[PROJECT]", "[DATABASE]");
  BeginTransactionResponse response = firestoreClient.beginTransaction(formattedDatabase);
  }
  </code></pre>
  
  @param database The database name. In the format:
  `projects/{project_id}/databases/{database_id}`.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails