Smartdown panopticon registry

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. 

Smartdown flows will register the equivalent information as previous Smart Answers, with the exception of `indexable_content`, this has been omitted because:
1/ For now we want to register draft routes so they can be tested on preview
2/ More thought needs to go in to how we extract text content from nodes.
3/ It's unclear (to me) how this text content is used, and how useful it is.

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


**Note**: This is branched from [refactor-smartdown-adapter](https://github.com/alphagov/smart-answers/tree/refactor-smartdown-adapter), which is still waiting on a merge (#1079). Merge this after.

Until thats merged it's best to [compare these changes](https://github.com/alphagov/smart-answers/compare/refactor-smartdown-adapter...smartdown-panopticon-registry) against that branch.

Additionally, this is dependant on a version of the Smartdown gem that hasn't been published yet, that will happen shortly, but until then tests are blocked :(