decapcms: enable Signed-off-by in commit messages

Enable the new config option introduced in [1] and released in
DecapCMS v3.12 [2].

[1]: decaporg/decap-cms#7766
[2]: https://github.com/decaporg/decap-cms/releases/tag/decap-cms%403.12.0

Signed-off-by: Simon Ser <contact@emersion.fr>

Author: emersion

static/admin/config.yml

@@ -7,6 +7,7 @@ backend:
     delete: 'news: delete "{{slug}}"'
     uploadMedia: 'news: upload media "{{path}}"'
     deleteMedia: 'news: delete media "{{path}}"'
+  signoff_commits: true
 site_url: "https://osrd.fr"
 media_folder: "static/images"
 public_folder: "/images"