Support of config bundles with extra configuration files

https://github.com/checkstyle/test-configs/tree/main/RegexpHeader/Example2
requires extra config file
`` (folder is not required we can update example to be just `java.header`)
https://github.com/checkstyle/test-configs/blob/670089984c086b21f75e11dfd493ac8205ad2404/RegexpHeader/Example2/config.xml#L20

Even we add it https://github.com/checkstyle/test-configs/commit/24f8a55bc31db0d761d76facee4b52979f08f676 like this.
it will not be downloaded, as we download only 2 files from test-configs repo.
and inside regression-report.yml of checkstyle we copy them to required folder for report generation.
https://github.com/checkstyle/checkstyle/blob/5eca53ce31f48b61fae0612a2092815009772b48/.github/workflows/regression-report.yml#L388-L394

We need to find a way to download all required files/folders and copy them to execution folder by regression-report.yml .

This feature will help a lot of modules, as several of them have ability to keep configs in separate files.

Use RegexpHeader/Example2/config.xml as the reproduction case, then inspect the download and copy steps in .github/workflows/regression-report.yml. Trace how the two current files are selected and placed, and verify that the extra config/java.header file and any required folders are available during report generation.】【。

Written by the indexing model from the issue text.