[Update] Update config.yaml to Address Deprecated Options

[Psycho0verload]

Description

While working on PR #275, I noticed that various options in the config.yaml are marked as deprecated and are slated for removal in future releases. The following warnings were issued:

/etc/borgmatic.d/config.yml: Configuration sections (like location:, storage:, retention:, consistency:, and hooks:) are deprecated and support will be removed from a future release. To prepare for this, move your options out of sections to the global scope.                                                                                                                                                             
/etc/borgmatic.d/config.yml: The checks option now expects a list of key/value pairs. Lists of strings for this option are deprecated and support will be removed from a future release.                                                                                                                                                                                                                                       
/etc/borgmatic.d/config.yml: The prefix option is deprecated and support will be removed from a future release. Use archive_name_format or match_archives instead. 

To address these, I've updated the config.yaml based on the official documentation here. The updated configuration works as expected, but without the deprecated warnings.