Support .config dir

[kevinwolfcr]

There has been recently community complaints about the amount of configuration files present on the root directory of a project, and some people are recommending to place all tooling configuration under a .config directory.

I personally think that, if Biome starts adding support for a .config dir, more projects could start adopting the practice too, since Biome is growing in popularity and encouraging reducing configuration overhead.

Reference: https://github.com/pi0/config-dir