Redirects: suggest redirect when changing a slug of a version

[stsewd]

What's the problem this feature will solve?

Changing the slug of an active version will delete its old documentation, leading to 404s, we want to suggest users creating a redirect after the change has been done.

Describe the solution you'd like

Suggest the creation of a redirect after the slug has been changed. Maybe in a message (ephemeral), or a notification (can be dismissed). That message can contain the values of the redirect that needs to be created (exact redirect, /{prefix}/{old-slug}/* -> /{prefix}/{new-slug}/:splat, we could also use some query params to prefill that information into the redirect form (/redirects/new?type=exact...).

Alternative solutions

404

Additional context

#11930