feature: GitHub Actions-compatible output format

[twpayne]

When running on GitHub Actions you can emit special commands that, for example, can be used to add annotations to pull requests. These annotations are displayed next to the file/line number in the PR's files changed view.

It would be great if, as a config option, editorconfig-checker could emit errors in this format, which is basically

::error file={name},line={line},endLine={endLine},title={title}::{message}

I would propose an OutputFormat config option in the config file with values either default or github-actions with a matching -output-format flag. When the value is github-actions the above format is used instead of the existing format.

I would be happy to create a PR for this if you want.