Improve OpenAPI docs

[tintamarre]

OpenAPI docs is not complete. https://api-ecli.openjustice.lltl.be/api-docs.html

All routes need to be documented and tested.

Documentation is done directly in controllers.

Example

https://github.com/openjusticebe/ecli-api/blob/master/app/app/Http/Controllers/Api/DocumentController.php