Consider patch mechanism for temp issues

[tidoust]

Build currently fails because one spec has an Editor's Draft link that targets the GitHub repo instead of the Editor's Draft. We can workaround the problem through a temporary override in specs.json. However, this means that we won't know when to remove the override.

A patch mechanism, as done in webref, would allow to detect when the problem has been fixed upstream, and thus when the patch needs to be dropped.