Support remote blackd server

Nobody has claimed this yet.

Our team is using a [remote blackd server](https://black.readthedocs.io/en/stable/usage_and_configuration/black_as_a_server.html), that's kept in sync with the version in CI. Some of our team members use VS Code, others use PyCharm. The latter has a plugin that let's the users set the path to a remote version of black, so that not everyone has to have a running version of the black server running and needs to keep track of that when we do a version bump on CI. It'd be great if this extension could add support for remote servers, since it's the biggest one for formatting with black.

I'm not sure how this extension currently handles black interaction (with blackd, it would look something like `curl -s -XPOST ":" -d ""`) and configuration (like line-length). Is the configuration passed with every request as with blackd or covered somehow differently? If that could be reused, that would be of course very nice.

Start by examining how the extension currently invokes Black and passes configuration such as line length. Compare that flow with blackd's HTTP interface, then define configuration for a remote host and port and verify that formatting requests use the configured options and return formatted Python code.

Written by the indexing model from the issue text.