Generate Warning that system has been downgraded

I made this in CE as I think it affects all distributions.

Until https://gitlab.com/gitlab-org/gitlab-ce/issues/57982 gets proven, we should figure out a way to alert customers that they have rolled back and that this is dangerous.

Maybe based on migrations or something, but yeah, it won't be happy times for now.

@marin I think you are the right person to chime in?