Smartdown panopticon registration

Updates version of #1089, which replaces #1093.

This PR extends the `panopticon:register` task also register Smartdown flows for routing. As with existing Smart Answer registration this respects status (published, draft, etc) per environment. Currently this means, `draft` permitted on dev/preview, `transition` not displayed anywhere yet (which is good, as that would make the student finance flow live on dev/preview)

Smartdown flows will register the equivalent information as previous Smart Answers, with the exception of `indexable_content`, which provides less content, but is discussed here: https://github.com/alphagov/smart-answers/commit/0e4ead604c95fcc727f7d068c7f572c7dcbd6349

It will only register a route once, so if both a smart_answer flow and a Smartdown flow share the same name it will pick the later. This is to match the app routing behaviour.

https://www.agileplannerapp.com/boards/203504/cards/5497
should we make coversheet available from smartdown flow interface?