default AsyncAdmin getAdmin() {
    return getAdminBuilder().build();
  }
Retrieve an {@link AsyncAdmin} implementation to administer an HBase cluster.
<p>
The returned instance will use default configs. Use {@link #getAdminBuilder()} if you want to
customize some configs.
<p>
The admin operation's returned {@code CompletableFuture} will be finished directly in the rpc
framework's callback thread, so typically you should not do any time consuming work inside
these methods.
@return an {@link AsyncAdmin} instance for cluster administration
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncConnection.java