[Jekyll] Add wildcards/regular expressions support to all options in _config.yml

<!-- Hi! Thanks for considering to file a feature request with Jekyll. Please take the time to answer the basic questions. Please try to be as detailed as possible. Thanks! --> ## Summary <!-- A one-paragraph explanation of the feature. --> My idea is to add wildcards/regular expressions support for all options in config file (`_config.yml`) that accepts file or directory (e.g. `include`, `exclude`, `keep_files`) ## Motivation <!-- Why do you want to see this feature in Jekyll? What makes you sure that it should not be implemented at the plugin level, but in Jekyll core? What use cases does it support? NOTE: Please be mindful of the Jekyll philosophy (https://jekyllrb.com/philosophy/), particularly Section 5. Think about if 90% of the users would benefit from your feature request, and whether your feature would be better off in a plugin. --> I think this feature should be added to jekyll core because most text/code editors create addi