Feature request: Cucumber "message" formatter replaces "json"

Thanks for a great project!! 👋

According to the README for cucumber-js, the json formatter is in "maintenance" mode and seems to be slightly discouraged: https://github.com/cucumber/cucumber-js/blob/main/docs/formatters.md#json

Note: this formatter is in maintenance mode and won't have new features added to it. Where you need a structured data representation of your test run, it's best to use the message formatter. Tools that rely on this formatter will continue to work, but are encouraged to migrate to consume the message output instead.

I'm not sure exactly how to map the former JSON output to the new message format.

The format is specified in detail here: https://github.com/cucumber/messages

Note: I don't actually need the richness of the message formatter. In my case, it's just a simple reporting tool that doesn't support the legacy JSON format and likely won't build an implementation for it.

No file or test is named. Start by locating pytest-bdd's formatter entry point and reviewing the linked cucumber-js formatter guidance and cucumber/messages specification. Done should be defined as a maintainer-approved way to provide the requested structured output, with tests covering the resulting format.