Once 8.1 base images (T372602) are available and multi-base-image "flavor" builds are available in scap (T370934), turn up a new 8.1-flavored deployment in the existing mw-debug namespace, along with LVS and DNS discovery services, etc.
In theory, once we fully migrate to 8.1, we can turn this all down again. Alternatively, we could keep it around, but scaled to zero, for later re-use when we migrate to PHP 8.3, etc.
If we go that route, we should give it a suitably generic name, e.g., "next" or "migration" or something.