[Feature-Request] Allow mypy.ini to be a dot file

[nioncode]

Currently, the default configuration files that are picked up are mypy.ini and setup.cfg in the current directory.
To remove clutter in the project root directory (where mypy's configuration is usually located), it would be great if .mypy.ini (i.e. with a leading dot) would also be supported and make the lookup-order: mypy.ini, .mypy.ini, setup.cfg.

It seems like most linters and formatters use dotfiles for configuration files (e.g. flake8, pydocstyle, pylint). There is already a way to use .mypy.ini through the --config-file command line argument, but it would be great if it would be picked up automatically, if it exists.

(On a side node, .mypy.ini is used with the dot when falling back to the configuration file in the user's home directory, so it makes sense to also support the dotfile variant in the current directory).