Support searching in .config folder

Is there an existing issue or pull request for this?

• I have searched the existing issues and pull requests

Feature description

https://dot-config.github.io/ extends the XDG standard to have a .config folder inside your project folder. It would be nice to be able to move the cliff.toml file into a .config folder to clean up the project root folder.

The main benefit of a shorter root folder is that Github displays the README higher on the screen by default.

Desired solution

Add .config/cliff.toml to the search path when looking for a config file.

Alternatives considered

None

Additional context

• bacon has added this already for its config file.
• I don't see this as useful for things like cargo.toml, which is the primary config file for the project, mainly secondary tools

Happy to PR this (it's probably not more than a few lines)