Create a failed login template.

Just had a client stumble upon this and the custom maintenance page and text made no sense in the context of failed login. They asked for a separate message / theme for failed login.

A separate template option would be great.

As a hack, I used a path-name class in the the body and hid the maintenance stuff and displayed blocked login stuff based on whether the path was `path-login`.

Done. I did not create templates for themes like Claro/Olivero here as I believe those are opinionated and should be their own issues. I also didn't create tests here as no messaging has changed.

What might be needed is a change record, as pages previously utilizing the maintenance page for this will now get a different template. Marking for review for now.

It appears there were tests around this already. Updated and added stable9 template as was expected as well.

Neat. Will definitely need a CR for the template addition.