🍀 Proposal: Support Config Dir #1328

What Would You Like to Add? Why Is This Needed?

Now we already support a single file as the config, why not support a directory?

Design

1. both support single config file and directory (no default value of -f flags)
2. if config is directory, read all .yaml or .yml files in that directory
3. if there is an invalid key in yaml files, an error should be reported

Anything else