Add defaults parameter to ColoredFormatter.__init__ in python3.10+

Python 3.10 added a `defaults` argument to the [`Formatter.__init__`](https://github.com/python/cpython/blob/3.10/Lib/logging/__init__.py#L567) to enable you to use custom fields in the format string.  Itʼd be nice if `ColoredFormatter` and `coloredlogs.install` supported this too.