* fix: "remove" a champ to prefill
Removing a champ to prefill on /preremplir used to fail, because of a
collusion (having the same form multiple times on un page looks like a
bad idea, when it comes to multiple input fields).
* fix specs
* feat(demarche): description
Show the description of an opendata procedure (published or draft),
with help about how to prefill a dossier for this procedure.
Co-authored-by: Damien Le Thiec <damien.lethiec@gmail.com>