Add composer.json to the module

Problem/Motivation

The module is missing a composer.json file. This is not a major problem, but it means that the module can be downloaded with the "composer require drupal/configuration_batch_export" command on a site, but cannot be installed if the drupal/config_suite dependency is missing on the site (mentioned in the .info.yml). By adding a composer.json file declaring the "drupal/config_suite" dependency, it would be automatically installed during the "compose require drupal/configuration_batch_export".