Support the glob pattern in `root_dir` and `model_dir`

[sinsoku]

We often want to specify multiple directories in root_dir and model_dir. For example, when using engines, packs-rails, etc.

• https://github.com/rubyatscale/packs-rails
• https://guides.rubyonrails.org/engines.html

This commit supports the glob pattern with these options, making it easy to specify multiple directories.

fixes #99

[sinsoku]

@drwl CI failed, so I fixed Style/StringLiterals and force-pushed.

[drwl]

@sinsoku just checking -- have you been able to try these changes in your local? I don't have a Rails app with packwerk setup to test.

[sinsoku]

@drwl I have tested it in a Rails app using packwerk. It worked with this change.

[jarredhawkins]

Also successfully tested this in a large Packwerked application. Thank you both for the contributions here!

[drwl]

Thanks for the confirmations @sinsoku and @jarredhawkins .