Add possibility to backup extra files

[donhardman]

First, we need to double-check if we truly need the configuration when restoring.

If the answer is yes, we should develop a system that allows us to pass multiple configurations, enabling us to back them all up. The feature should also allow us to add extra files to the backup if needed for restoration.

This is based on requirements from out official Docker image.

[donhardman]

The feature has been added to the backup project, allowing us to back up multiple files using the syntax: --config=path-to-config1 --config=path-to-config2.

We use the first config for communication and back up all other configs.

MANTICORE_CONFIG also supports multiple configs but can also accept a single one. To pass it in an environment variable, use | as a delimiter and define it as a string.

Restoring will recover all configs in the backup without needing a specific config.

We must ensure this change doesn't cause any issues and that we implement tests to verify its functionality.

Here's the pull request: https://github.com/manticoresoftware/manticoresearch-backup/pull/106

[donhardman]

It's been implemented and merged, so I'm closing this issue. However, we still need to add tests. Here's the link for reference: https://github.com/manticoresoftware/manticoresearch-backup/issues/107